Arashi Kishu in X1999. In order to spare her lover Sorata from his obligation to sacrifice himself for her, she joins the Dragons of Earth to bypass fate. She battles her former Dragons of Heaven friends and eventually triggers said prophecy with her Face-Heel Turn. In the anime, Sorata dies anyway in her arms, but manages to make her return to the Dragons of Heaven. In the manga, by all appearances, Arashi ends up Brainwashed and Crazy at the hands of Hinoto's Superpowered Evil Side. With the same result, fighting for the Dragons of Earth.
If there's going to be an X1999 example, it ought to be Kamui and Fuma. They were best friends as children, and destined to be on opposite sides of the battle for the future of mankind. Whichever side Kamui chose, Fuma would automatically take the empty seat on the opposite side as a substitute "Kamui".
Ash Ketchum and Gary Oak of Pokémon fame. They were good friends and neighbors when they were very young. It's explained that they fought over a Poke Ball they found and broke it, and stopped being friends over it. It turns out each kept his half of the Poke Ball, and they are on better terms again.
Berserk - Guts and Griffith used to be the best of friends during the Golden Age arc. Then Guts left the Hawks in order to pursue his own dream, and Griffith's life went straight to hell, and by the time that Griffith was rescued, he all but despised Guts. Guts, however, still held on to his feelings for Griffith up until the Eclipse, where Griffith's monstrousbetrayal would destroy the bond of friendship between the two men forever.
In Neon Genesis Evangelion, Ritsuko and Misato has been friends since college, but the events of the series causes rifts between the two, leading to frequent (and sometimes physically violent) arguments about how to handle situations which could endanger the pilots, and it doesn't help matters that Misato slowly come to realize just how much Ritsuko have kept her in the dark about NERV's rather disturbing secrets. In the latter part of the series their relationship is constantly teetering on the edge of fully turning into this trope, and it is pretty clear at this point that Misato only stays on speaking terms with Ritsuko because there aren't too many others around to talk to any more. What little that remains of their old friendship finally ends in Episode 23, as Risuko reveals the truth about Rei, and destroys the Rei clones.
In the third Rebuild of Evangelion movie, the protagonist wakes up to a world where all of his former comrades, friends and coworkers hate his guts, express their hatred and mistrust in ways ranging from passive-agressiveness to outright venting at him, strap a bomb collar to his neck, refer to him by a test subject number and put him in a cell without explanation. The reason is later revealed to be that he was set up by the villain to render the planet almost completely uninhabitable, and that in the ensuing 14 years he spent as a Human Popsicle, everyone pretty much forgot what he meant to them before they only knew him as "That thing that's to blame for us living in a Post Apocalyptic Wasteland". While there are residual feelings on bothz sides - his former Parental Substitute can't bring herself to kill him - their bonds are pretty much unrecoverable.
Pretty much the whole point of Part 2 in Naruto. Sasuke Uchiha is the patron saint of this. Even his new allies who were ready to give their lives for him were quickly discarded.
What's interesting in this case is that Naruto's devotion to saving Sasuke - in one form or another - actually causes breaks between him and his friends, who think Sasuke is an evil back-stabbing bastard who needs to die. So essentially Sasuke has instigated a chain reaction of this trope.
Even before that, we have Ino Yamanaka and Sakura Haruno stop being friends because they are competing over Sasuke (who doesn't much care for either one of them). They become friends again after fighting each other (which, at least to Sakura, was more about proving herself equal to Ino, whom she had held in high regard ever since she met her, than about Sasuke), but do still quarrel over Sasuke from time to time.
Jiraiya and Tsunade with Orochimaru. Jiraiya confronts Orochimaru during his escape from Konoha, and reminds them that the Sannin were friends since their team was formed when they were five years old, but Orochimaru mocks his efforts.
In Naruto, this goes way back to the First Hokage and Madara Uchiha. The latter, who is the Bigger Bad of the series and a Manipulative Bastard while being dead, had fantasized as a kid with the former about creating a place where children wouldn't be sent to die in war. As an adult, after temporarily giving his old dream a shot, he named the Hidden Leaf Village.
Code Geass Suzaku Kururugi and Lelouch Lamperouge were friends in childhood but separated during Britannia's invasion of Japan. When they met as young adults, they were on opposite sides of Japan's war for independence, although it takes them a while to realize this. Things only get worse when Lelouch accidentally Geasses Euphemia, the woman Suzaku loved, into committing genocide, and then kills her himself.
Happens to Yomi and Kagura in Ga-Rei Zero-, the prequel anime to the manga. Yomi's fall is pretty heartbreaking, and they only further make it more painful by the Big Bad who unleashes an attack on Yomi which doesn't kill her, but severs her voicebox and nerves so she's only barely able to communicate by using her finger, and can't speak. The scene where she's trying to cry in the hospital after her fiance is forced to break off their engagement is particularly heartbreaking.
Tower of God: Baam and Rachel. In this case, it doesn't end well, and the falling out started before Baam even realized it: The moment he followed her into the Tower. In the end, she drowns him and he barely survives, crushed by the fact that his only family, friend and possible lover now hates him, where the only thing he truly feared was being alone.
Miaka and Yui in Fushigi Yuugi. Yui becomes Miaka's worst enemy after Nakago manipulates her into believing that Miaka doesn't care about her or her feelings for Tamahome.
A major force of tension in Mobile Suit Gundam SEED is the fact that the two protagonists, Kira and Athrun, are best friends who have somehow wound up on opposite sides of a war. There is a great deal of introspection between the two of them about what this means to their friendship, how each other have changed, and why are they really fighting anyway? Eventually they both decide to Take a Third Option and wind up as part of the Three Ships Alliance, on the same side once again.
The second-gen story of Mobile Suit Gundam AGE revolves around Asemu Asuno and Zeheart Galette, who befriended each other when Zeheart (a Vagan) went undercover in Asemu's high school to find the Gundam (which is the Asuno family's raison d'etre). Soon enough, Zeheart reveals himself and returns to his side. He and Asemu are really conflicted about fighting each other, end up working together to prevent a Colony Drop, but in the third generation Zeheart goes over the edge and only reconciles with Asemu during a fatal duel that Asemu wins. An OVA, Memory of Eden, was made to further expand the Asemu—Zeheart story.
Muhyo and Yoichi with Enchu. The three were close friends in the academy, but Muhyo and Enchu were considered for the position of Executor; Enchu was desperate to get the position so that he could support his sick mother while Muhyo didn't want it. Enchu losing his mother and the position in quick succession was his Start of Darkness, as he became obsesssed with revenge against Muhyo.
Page and Tomas used to be friends before Tomas's evil nature became apparent.
Mariko and Aya in the anime of Oniisama e.... They got along in junior-high, but one day Aya threw Mariko under the bus in a school competition, and things never were the same from then on.
The "master and apprentice" variation of this went on in the Soul Society arc of Bleach between Yoruichi and Soi Fon, as Soi Fon worshiped the ground upon which Yoruichi tread before the latter fled for 100 years in an incident that made her an outlaw, leading to Soi Fon to swear that she would surpass Yoruichi and bring her in personally, although it is indicated that Soi Fon has forgiven Yoruichi. Canon is hazy about whether this is a Les Yay thing, however, which would change the dynamic significantly.
The thing is, it wasn't incident itself that Soi Fon was mad about: It was the fact that Yoruichi didn't take her with her when she left.
In Mai-HiME, Shiho and Mai got along well early on in the series, with Shiho asking Mai to root for her attempts to win Yuuichi over. Midway through the show, however, Yuuichi tells Mai he has feelings for her with Shiho in earshot, and Shiho accuses Mai of lying to her and tries to kill her when her Hime powers awaken, even going so far as to kill Mai's younger brother out of spite.
In Axis Powers Hetalia we have America and England. Theirs is an interesting case, because even though America betrays England, it's done for political reasons, not because he hates him, and England is broken by it, but can't bring himself to kill him because he still loves him. Then, after hundreds of years they start to mend their bond. The shippers are not shy about what they think of all this.
In the webcomic form of the series, there was also Japan and China. China raised Japan as his little brother, only for Japan to break away by attacking China with a katana.
In Fist of the North Star, a lot of the Manly Tears shed when Kenshiro and Raoh fight are because they both know that they can only win by killing their brother. Even when Kenshiro is ultimately victorious, he chooses to remember Raoh as the beloved brother he used to be.
The third drama CD for Puella Magi Madoka Magica showed that Mami and Kyouko, who were shown together in the series itself for all of two scenes (either in alternate timelines or after Madoka erased all witches) used to be close in something like a Sempai/Kohai relationship before a very personal tragedy befell Kyouko, which soured her personality so much she left. In The Different Story, Mami and Kyouko do interact, as Mami lived longer than in canon, and things are largely awkward because of their differences, although they do seem to care for each other.
This is the relationship between Jacques Durant and General Henri Guisan in Honoo No Alpen Rose. Ever since childhood, they were Vitriolic Best Buds: always squabbling, but always by each other's sides. Until they disagreed horribly about the subject of Durant's daughter Helene's Arranged Marriage: Guisan not only opposed to have the girl not choose her future husband, but he helped Helene escape from the engagement. Durant blew up at him when he found out, and they cut each other off. And since few years later the Durants fell in the hands of Toulonchamp the Arms Dealer, Guisan cannot forgive himself for not having been there for his once best friend.
In the New 52, Aquaman and his brother Orm (Ocean Master), are portrayed as having been very close as teenagers, and when Arthur left the throne, Orm begrudgingly took his place. The relationship deteriorated when Orm attacked the surface world, forcing the Justice League into action, thus forcing Arthur to pick a side (he was talking both sides down). Afterwards, once Orm is imprisoned, they still don't particularly hate each other, but it's just the way it has to be.
Depending on the mythos of that universe — and Depending on the Writer — Charles Xavier and Erik Lensherr (Professor X and Magneto, respectively) started out as best friends and bosom buddies, until they broke off because of differing opinions (Charles with the opinion that mutants and humanity are not enemies and Erik believing they are with mutants poised to become the dominant force).
In at least one universe, the 'bosom buddies' business caused (or at least helped) both of their respective marriages to break up. This has not helped the people who protest the Ho Yay between the two at all.
The Juggernaut and Black Tom Cassidy from, thanks to Juggy's Heel-Face Turn.
Colossus and Magik. Especially after he sacrificed everything (including his humanity and the love of Kitty Pryde) to save her from evil by taking on the power of Juggernaut only to find that, after her time in Belasco's Limbo, she had embraced evil, and only encouraged him to become the Juggernaut so he would become as damned as she was. When last he saw her, he promised, "If I ever see you again, I will kill you."
Wolverine and Sabertooth, for apparently over a hundred years. But ten Wolvie's got Creed's girlfriend killed, taking away his happy ending, and Creed swore to dedicate his life to making sure Logan would never get one of his own.
Spider-Man: Peter Parker and Harry Osborn. Their rivalry took place in the aftermath of the death of the original Green Goblin, Harry's father, and led to Harry going crazy and becoming the second Green Goblin. That a boobytrap set for Peter almost killed Harry's ex-girlfriend Mary Jane probably was seen by him as a positive side-effect.
In All Fall Down, the Pantheon tries to reason with Pronto this way. They don't quite succeed.
Steve Rogers and Tony Stark in Civil War, which was basically portrayed as a particularly volatile break-up/divorce. With Steve coming back from the dead, their relationship has since improved, not a little because fighting each other tore them both up pretty badly in the first place.
Watchmen Rorschach and Nite Owl II/Dan who were crime fighting buddies before the novel, now share a tensed relationship. Rorschach even somewhat disdains Dan's lifestyle, but as the story progresses they partly rebond and face the Big Bad together.
Subverted in Green Lantern Wrath Of The First Lantern with Sinestro and Hal Jordan. Hal asks Sinestro if they were ever truly friends. Sinestro responds with, "That's the tragedy of all this. We'll always be friends."
The entire point of the the sadly discontinued NanohaDark Fic 'Betrayers', which divides the cast into a bloody civil war. Spoken practically word for word by Fate.
In the Jackie Chan Adventures fic Queen Of All Oni, after Jade turns evil once again, her family and friends still care deeply about her, to the point that they are willing to FIGHT her so that they can return them to normal, even though her feelings towards them have been twisted by Daolon Wong's faulty spell, especially towards Tohru, since he became Uncle's apprentice instead of her.
In the Katawa Shoujo fanfic Reconciliation Hanako has this with Lilly and Hisao. The fic takes place after her bad ending, in which she snapped over being pitied by Hisao and angrily said she hated him and Lilly, then isolated herself from them out of guilt. This leads to an awkward moment when Hanako introduces her publicist and friend Sho to Lilly, who is unable to describe Hanako as anything more than someone she knew in high school, despite never having been angry with her for how she acted. By the end, the two have renewed their friendship and Lilly visits Hanako in Japan to catch up.
Obviously crops up in Inner Demons, as the entire plot is driven by Twilight Sparkle succumbing to her Enemy Within and becoming the new Big Bad her friends have to fight.
Also an element in Apple Bloom's subplot. Her friendship with the other Cutie Mark Crusaders (primarily Scootaloo) falls apart after an argument in which she makes it clear she wants to take her search for her Cutie Mark more seriously. Later on, Scootaloo and Sweetie Belle are talked intoFace Heel Turns, while Apple Bloom stays on the side of the protagonists. Notably, Sweetie Belle clearly still cares about their friendship and wants it back which is why she tries to talk Apple Bloom into switching sides as well.
In Weekend at Hisao's, Hisao ends up encountering his friends who, in the prologue to the game, stopped visiting after a few weeks, and hears that they have a get-together planned with his former crush Iwanako. It takes some coaxing from Shizune and Misha before Hisao decides to attend, but the meeting goes fairly well and his old friends end up getting invited to his wedding a few years later.
Rainbow Dash: Gilda! Tell me, why are you doing this? We used to be friends!
Gilda: That’s right, Dash! We used to be! But you chose those ponies instead of me!
In the Ponies Of Olympus series, Rarity and her rival Ran Biao used to be friends when they were growing up together in Lao Wu's dojo, until Ran Biao grew jealous over Rarity's superior talent, and crossed the line by seducing and stealing Rarity's Love Interest Razorwing. Rarity never forgave her for that, and they've hated each other ever since.
In the Axis Powers Hetalia fanfiction Ignorance, My Bliss, the nations get energy boosts by drinking each other's blood, essentially making them all addicts. They discover that no one has fed off of America ever, meaning that his blood will give them a lot of strength, and don't hesitate at all to chase him down and drain him of his blood. Japan even tells America that though they're friends, his blood is just too tempting. And then, it turns out that even Canada turned on America, only pretending to save him so he'd have a chance to get him alone.
In Necessary To Win, Ami and Takako follow this trope. They were friends since they joined the Nishizumi School together, until Ami's disagreement with Takako over the latter's harsh methods of discipline as coach of Black Forest drove a wedge between them. Both remain close with their mutual friend, Kikuyo, though.
Films — Animated
In The Prince of Egypt, Rameses and Moses were raised as brothers. They became enemies when Rameses was Pharaoh and Moses returned from hiding to free the Hebrews from bondage.
"You who I called brother,
how could you have come to hate me so?"
Films — Live-Action
Star Wars: Taken to the extreme in Revenge of the Sith, the third film of the prequel trilogy during the battle between Anakin Skywalker and Obi-Wan Kenobi. See quote above.
13 Going on 30 deals with this. Jenna abandons Matt when she becomes more popular. They reconcile, though. Has something to do with Time Travel.
In Fire Over England, Sir Richard Ingolby, the English Privateer, unknowingly attacks the galleon of his former friend, Don Miguel de Casanz — when they encounter each other in battle, Ingloby tells his son, Michael, "We were friends once." "Enemies now!," shrieks Michael, and attacks.
The film details the relationship between James Howlett (Wolverine) and Victor Creed (Sabretooth), who are half-brothers. They were Bash Brothers to the very end until Victor's sociopathy went off the deep end and caused James to lose his connection with Victor.
Victor also kills his old teammates.
The whole premise of X-Men: First Class is to show how Charles Xavier and Erik Lehnsherr became friends and then ended up on opposite sides with different ideals. There's also a subplot about Raven's fallout from her relationships with Charles and Hank. It's a theme in the original trilogy as well, where they are Friendly Enemies and the beginning of X-Men: The Last Stand depicts younger - and closer - versions of them, when they were still working together.
Mark Zuckberg and Eduardo Saverin in The Social Network were once good friends but after Mark had Eduardo kicked out of the company, all bets were off.
Downplayed in the Alterien series. Abigail asks Oberon if Ulysses River, a superhuman assassin who just tried to kill his sister, and he were friends. Oberon replies very matter-of-factly they were not friends, only teammates.
Played straight in the Astral Dawn series. Caspian Knoll and Ciaran Devlyn were once the best of friends in another life. After their deaths, Caspian went on to be reborn in other lives while Devlyn went straight to Hell. That put a pretty big gap between the fellows who would eventually become deeply at odds over the fate of Celestial City.
In Memoirs of a Geisha, the friendship between Sayuri and Pumpkin became strained once two rivals, Hatsumomo and Mameha, adopted each of them. And once Sayuri became more popular than Pumpkin, even having Mother formally adopted her, Pumpkin grew envious.
Peter Pettigew in Harry Potter. The other surviving Marauders view him with extreme disgust for siding with Voldemort.
In Warrior Cats, Fireheart and Onewhisker were friends ever since they were both young warriors. When Onewhisker becomes leader of WindClan, he is harrassed for being such a close friend to a cat of another Clan that he breaks off the friendship and views them more as enemies than anything.
The classic Dutch novel Oeroeg exploits this trope for drama in the relationship of the two main characters, a white Dutch boy of a rich family and a native Indonesian boy of a servant family. They grew up together, seperated during high school and when the main character finally returns to Indonesia (during the 1940s uprisings) he is told by his former friend to leave since he has no more business in the country.
In The Saga of Darren Shan Darren and his best friend Steve were an in separable duo but little did they know destiny had other plans for them.
The Age of Fire series has RuGaard and NiVom. They were close comrades during their years in the Drakwatch together, but the relationship soured after the political intrigues of the Lavadome saw NiVom exiled and RuGaard made Tyr (a position that should have been NiVom's).
24: One of the plots between Jack Bauer and Tony Almeida in the seventh season. Although the two originally started off on bad terms, Tony eventually became one of the very few people Jack personally trusted with his life. By season seven, a broken Tony has discovered the true identity to the conspiracy that led to the death of his family and his ties to the government, leading him to resort to terrorism in order to get the guy. Jack rightfully sees Tony as a traitor to his country betraying the memory of his loved ones, and Tony in turn sees Jack as nothing but a sellout and a hypocrite by continuing to work with the same government they've both lost faith in.
The Reveal that Ward had been Evil All Along came around two-thirds of the way through Season 1. Instead of killing him off in the finale as was originally planned, the writers were impressed enough with Brett Dalton's performance that they decided to keep the character in the main cast. They do this by having the rest of Team Coulson keep him prisoner on their new base, using him as an informant against HYDRA.
Due to the HYDRA uprising in Season 1, this becomes the case for a lot of regular characters within S.H.I.E.L.D., most notably John Garrett and Jasper Sitwell. Unlike Ward, however, they're all dispensed with by the finale.
Wesley Wyndam-Pryce. After Wesley translated a prophecy that predicted for Angel to kill his son, Wesley took the child to save his friend from his horrible fate. When he was about to leave town with the boy, he got his throat slit by The Dragon of Angel's nemesis and the baby was now taken from him and brought to a Hell dimension. His friends didn't take it that well. As a result to this, his friends never wanting to see him again, as well as the revelation that the prophecy he was trying to prevent was in fact fake and that he sacrificed everything for nothing, he takes a major in Badassery and is from then on very reserved concerning his former friends.
Gunn: What happened to you, man? Wesley: I had my throat cut and all my friends abandoned me.
Wesley: I have no idea where Angel is, Lilah, or what happened to him. And I really couldn't care.
Lilah: Wow. That was cold. I think we're finally making progress. Come on. Doesn't it bother you just a little bit? The not knowing?
Wesley: That part of my life is dead. Doesn't concern me now.
Subverted: He was looking for Angel the whole time.
Double Subverted: After he finds him, he still stays the hell away.
Wesley steadily reconciles with them during the fourth and fifth seasons, however - despite the pain of what happened, Angel later states that overcoming this trope made their friendship afterward stronger than ever.
Also happens in the second season, when Angel fires Wesley, Gunn and Cordelia from Angel Investigations.
Arrow: Oliver and Slade. They became close friends and allies when trapped on the island, but between exposure to Mirakuru and Shado's death, Slade came to hate Oliver.
General Hague is killed in battle after organizing a mutiny against President Clark's authoritarian regime. It's mentioned that the attacking ship was captained by a close friend of Hague's who had known him at the academy but nonetheless had remained loyal to Clark. The other officer is presumably killed when Hague's ship destroys it soon after. Major Ryan warns that this will be the case for most of their enemies in battle now.
Apollo and Starbuck from the remake are a looping On-Off-Couple/Friends. When the fleet reaches New Caprica however and Apollo and Starbuck sleep together they seem to share a now very distant relationship. We only learn later on why.
Happens to the Old Man and Col. Tigh. Twice actually. The first time when the exodus from New Caprica succeeds and Saul can't really deal with what happened, the second time when the XO reveals to Admiral Adama that he has been a Cylon all the time. They manage to reconcile eventually.
Black Adder fans have a popular Head Canon theory that Captain Blackadder and Captain Darling were good friends before the war started, but they fell out after Darling got out of being in the trenches to be General Melchett's PA.
This really becomes a Subverted Trope because scenes showing him in a mental institution afterwards show that after the initial shock, his friends are actually very supportive, visiting him and trying to help him recover. They know that he's still their friend, he was just indoctrinated by what passes for an Evil Mastermind into doing his bidding because, despite his high intelligence, he is ridiculously naive and was taken advantage of. Everyone is more...baffled than feeling betrayed.
Buffy left her friends after she had to kill Angelus/Angel seconds after his soul was restored. She took off to Los Angeles, leaving her friends behind. Her return to Sunnydale is awkward - at best.
The entire point of Faith becoming The Dragon to the Mayor.
Cordelia also fits since 'Lovers Walk'. Though she doesn't fully repair her vitriolic friendship with the Scoobies completely, however, they manage a reconciliation by the end of the third season, and all interactions between them from then on are on generally good terms.
Rupert Giles and Ethan Rayne.
Willow when she turned evil for a part of the series.
Doctor Who: The Doctor and the Master were at school together back on Gallifrey, and are still on Friendly Enemy terms most of the time. The Third Doctor called the Master his best enemy and openly looked forward to their meetings. The Tenth Doctor's finale featured reminiscences of their shared childhood. Apparently the Master was a rich boy: his father had estates where they would play together.
Friends: Briefly lampshaded in the fifth season, when Ross tries to work things out with Emily by agreeing to never see Rachel again. Rachel convinces Phoebe to set up a new 'group' with her. It didn't happen.
Gossip Girl: Serena and Blair at the very beginning of the series.
Pretty much happens all the time due to the fact of bonding and scheming. But especially Dan falls in this category when publishing his books / exposès.
LOST: Michael is another good example. During Season 1, he seems to be a nice and well-liked member of the Losties. When his son Walt is kidnapped in the Season 1 finale, he knocks out Locke and Jack in order to get a head-start going after the Others. When he returns eventually, he decides to betray his friends and lure them into a trap to retrieve Walt.
Merlin: Morgana discovers that Arthur is her half-brother in the third series and spends the remainder of that series and all of the next trying to kill him so that she can consolidate her claim on the throne. When they finally come face-to-face at the end of series four, Arthur sadly asks her: "What happened to you, Morgana? I thought we were friends." When Merlin asked her a similar question in series 3, she replied that she hasn't forgiven him for poisoning her. This trope is the only reason Merlin hasn't killed Morgana.
Ryan Atwood at the end of Season 1 and the beginning of Season 2 - oh, and the beginning of Season 4. Leaving the Cohens after Marissa's death, becoming a cage-boxer, driven by revenge and grief along to Placebos 'Running Up That Hill'.
Seth claims to not care about Ryan and his family anymore, as they try to persuade him to come back to Newport at the beginning of Season 2. They manage to reconcile quickly.
Once Upon a Time: Snow White and the Queen, though due to the age difference it was more a niece and cool aunt relationship. As Snow White grew older and the Queen grew more bitter in her loveless marriage to the King, the two grew to hate each other. Also, the Queen blames Snow White for being tricked by the Queen's mother Cora into spilling the beans that the future queen was in love with Daniel the stable boy, leading Cora to kill Daniel to force her daughter to marry up.
Revolution: As revealed in episode 3, captain Jeremy Baker with Miles, during the founding of the Monroe Republic. Not to mention Miles and Monroe, as shown in flashbacks in episode 10.
Scrubs: Also happens. Especially to Elliot and JD at the beginning of the fourth season. A milder case of the trope though. Their second attempt at a relationship ended badly and for a while they had a "superficial friendship", being generally friendly but not nearly as close as they once were. They became roommates, which brought them a lot closer.
The Shield: With the end of Season 3 and the disbandment of the Strike Team, the relations between its former members are heavily tensed. Especially Shane, who seems to have crossed the line, thinks very differently about his former best friends:
Army: "Jesus Christ. Lem's one crazy-ass white boy. You really used to be tight?"
The angel Balthazaar, a former friend of recurring character (and fellow angel) Castiel. At some point during the Apocalypse, Balthazaar went rogue and has started making deals with humans for their souls. When Castiel discovered this, and Balthazaar tried to get him to do the same, he stated how disgusted it made him, and declared the two of them enemies.
Gabriel and Lucifer. They used to be very close, as Lucifer claims that he taught his little brother everything he knows. Lucifer then kills Gabriel because Gabriel sided with humans.
Near the latter end of Season Six, Sam and Dean discover that Castiel is working with Crowley to gain control of Purgatory and all its souls. Castiel tries to justify his actions, but the brothers want nothing more to do with him (especially as of the season finale, where he jumped off the slippery slope). In an interesting inversion of the previous example, when Balthazaar discovers what Castiel is up to, he is horrified at what his friend is becoming, and starts spying on him for the Winchesters. This ends up costing him.
Castiel is The Atoner in season 8 and starts repairing his friendship with the Winchesters, although this is complicated by his also being a Manchurian Agent for Naomi.
CM Punk was besties with Paul Heyman. Yeah, thatPaul Heyman. When Paul inevitably betrayed him, Punk was beating himself up for grabbing the Idiot Ball and not seeing it coming, as being his best friend he should've known that Pauly would sell out his own mother if he saw the writing on the wall.
Rent - Roger, Collins, Maureen and Benny used to be tight when they were roommates, but when Benny moved out, bought their building and married Allison, a rift grew between them when it became clear he no longer thought the same way they did. Maureen hates Benny for "no longer believing in the same things." Mark and Roger hate him both for abandoning them after Roger got sick and for reneging on their deal. They all express themselves childishly. It's a stupid old world all around.
Inherit the Wind features a scene where Henry Drummond and Matthew Brady, opposing counsels in the trial over evolution, meet and muse over their past friendship. It's stated that their differing views on religion caused them to party ways.
Frank, Charlie and Mary had a tight friendship in Merrily We Roll Along until Frank made it big and the other two interpreted it as selling out.
Final Fantasy II: Firion, Maria and Guy with Leon. Even at the end, after his Heel-Face Turn, he suggests that too much has happened for them to go back to the way they were before, but Firion holds out hope.
Final Fantasy VII: Cloud and Sephiroth. Or at least that's how Cloud initially frames how they know one another. In reality, Cloud and Sephiroth were never friends, but Zack and Sephiroth were and did act out this trope.
And in Crisis Core Zack and Angeal in addition to Sephiroth and Genesis.
Metal Gear Solid 4: Big Boss and Major Zero's We Used To Be Friends is partially the cause of the Metal Gear Saga. Over time, they went from close friends to the most bitter of enemies. Why? because they were both so arrogant in their opposing (wrong) beliefs about what their idol, The Boss, wanted for the world that they each went to extremes to fulfill their personal interpretations, dividing The Patriots and causing Zero to create Solid and Liquid. Whilst at the end Big Boss no longer feels hate for his old comrade, it is far too late for them to repair their friendship as Zero's advanced age had left him a brain dead shell.
Shepard and the Virmire Survivor in Mass Effect 2. Joining up with terrorists (no matter how noble your intentions) will do that.
Worse at the start of Mass Effect 3, although they're prepared to hear you out. Depending on whether you take the time to clear the air, they can end up rejoining you, going to work with Hackett or dying at your hands. That last one's not too hard to avoid, though.
In Ace Attorney, Phoenix Wright and Miles Edgeworth were part of a Power Trio with Larry Butz during the fourth grade after Miles and Larry were the only ones to stand up for Phoenix when he was accused of stealing Miles' lunch money. It was Larry. When something smells, it's probably the Butz. Then Edgeworth switched schools after his father was murdered and switched career goals from defense attorney to prosecutor. Phoenix was inspired by Edgeworth and Butz to become a defense attorney himself, which led to a legendary courtroom rivalry between Wright and Edgeworth. They do become somewhat friends by the final case of the first game when Edgeworth actively helps Wright get the true killer of a case to confess.
This also happens with Lana Skye and the rest of the SL-9 investigation team. Because she was blackmailed by Gant into fabricating evidence, and she became cold and distant as a result, Angel Starr and Jake Marshall became quite bitter toward her.
In Dead or Alive Dimensions, a few scenes suggest this of Kasumi and Ayane, as flashbacks show the two playing together, and their mother, Ayame, tells Ayane that they used to get along quite well, and hopes they will again.
In Tales of the Abyss, Jade and Saphir (who now goes by the name Dist the Rose) are this trope, although Jade denies it and Dist claims to regret it ever having been true. Their past association was broken when Jade chose to abandon fomicry due to personal and ethical concerns, while Saphir refused to stop trying to revive Professor Nebilim, considering Jade a traitor for giving up too soon. The party speculates they like each other better than either wants to let on, and it's usually Played for Laughs.
In Guild Wars 2 this is the current state of the (surviving) members of Destiny's Edge, the Five-Man Band of Living Legend s that takes up a lot of the backstory. The human member of the group abandoned them during a crucial battle to save his queen, which ended up getting one of their members killed. He is saddled with the brunt of the blame for what happened, but it also brings out and creates a lot of resentment for some members towards others, and they drift apart. Particularly tragic since the group was quite important in the whole overcoming racial barriers department. A large part of your characters personal story is based around getting the band to overcome the bad blood and get back to the whole saving the world from dragons business. (It is an MMO after all, obviously that task couldn't lay on your shoulders alone.)
Katawa Shoujo has Lilly and Shizune, who are also cousins. Lilly joined the Student Council when most of the older members had left, but got into many arguments due to their personalities clashing (Lilly thought Shizune was too harsh and tyrannical, while Shizune thought Lilly was too unreliable). In Lilly's route, the two reconcile shortly before Lilly is to leave Yamaku. In Shizune's route Shizune admits that she was in the wrong.
In Knights of the Old Republic Revan and Malak used to best friends, till they were corrupted by the Sith Emperor. Then the dark side of the force did the rest.
Rios: I've changed my mind. I don't want to see that fucker's face again.
Alpha: You managed to even make Rios hate you, you evil sack of shit
In Portal 2, Wheatley attempts to exploit this to make Chell stop running away from his Death Trap. Being Wheatley, it's not very subtle.
"Aw. Just thinking back to the old days when we were friends. Good old friends. Not enemies. And I'd say something like 'come back', and you'd be like 'no problem!' And you'd come back. What happened to those days?"
Sora and Riku from Kingdom Hearts. Riku becomes a major antagonist after Maleficent manipulates him into believing that Sora doesn't care about him or his feelings for Kairi. He soon snaps out of it, and his friendship with Sora is restored. Of course, Sora never thought of Riku as an enemy, and after he saves Kairi, is determined to rescue him.
Sadly played straight with Aqua to her friends Terra and Ventus, though in both cases, they are possessed. And with Master Xehanort towards Master Eraqus, to the point of using Terra, who sees Eraqus as his father, to weaken him.
Axel and Saïx, back when they were Lea and Isa. As they grew up and became Nobodies, Saïx became crueler due to Xehanort's Grand Theft Me and Axel befriended Roxas and Xion instead. This all comes to a head in 3D, where Isa has been completely taken by Xehanort and attacks Lea without hesitation at the climax of the story.
The Elder Scrolls V: Skyrim: Ulfric Stormcloak, Galmar Stone-Fist, and Legate Rikke were once friends who fought together in the war against the Aldmeri Dominion. In Skyrim's Civil War, however, Ulfric and Galmar lead the Stormcloak rebellion and Rikke works with the Imperial General Tullius to put said rebellion down. There is no happy ending for them. If the Stormcloaks win, Ulfric and Galmar all but plead Rikke to surrender so they won't have to kill her, but she refuses. If the Imperials win, Rikke still hopes to the bitter end that Ulfric will see reason and surrender, but is forced to fight him and Galmar to the death when he also refuses.
The Wizard and the King in Teslagrad used to be staunch friends and allies, but then the King began to abuse the powers the wizard had given him...
In Shovel Knight the titular character and Polar Knight used to be friends. Both encourage the other to change allegiances before fighting, and even after his second defeat the Polar Knight still believes Shovel Knight should join the Order.
There's also Black Knight. Prior to the events of the game, they were in the same team as Shield Knight and Black Knight's attempts to hinder Shovel Knight were meant to prevent him from killing Shield Knight (who has become possessed by The Enchantress).
Petra and Jinjur from Emerald City Confidential have this dynamic when the two part ways after their army days. Jinjur is bitter because Petra abandoned her post and duties during the Phanfasm War to find her missing brother. Petra is bitter because the Ozian royal guard never helped her search for him.
Retroactive example in Homestuck: Vriska actually used to be pretty close to Aradia and, in particular, Terezi, but after she started going too far and becoming Chaotic just for the sake of it, both turned their backs on her, their relationship irretrievably broken. Even later when Terezi remembered their friendship and wished they could return to it she couldn't pretend that Vriska wasn't evil or that she wouldn't work against her if it was necessary.
Gamzee and Karkat were moirails after Karkat pulled him out of his murderous rage. During their isolation on the meteor, Karkat makes a point that he won't reveal where Gamzee is, and Gamzee admits to wanting to keep his relationship with Terezi secret because he fears for their friendship. When they finally get to the Post-Scratch Kid's session, their relationship has fallen apart because Gamzee didn't hold up his end. When they meet up again on LOFAF and Karkat sees him viscously beating Terezi, he makes it clear that Gamzee's gone too far.
In Evil Plan'' Stanley Kinesis, (back in college) and William sever ties after a fight about the telekinetic chip. Possibly subverted, as it was recently revealed that they're still on speaking terms. Why this is has not yet been explained.
In Sonic the Comic Sonic and Amy were friends but in Sonic the Comic – Online! after the Kane arc Sonic and Amy have become enemies (although it is implied Amy still trusts Sonic on some level, it's just impossible to be sure about him given the circumstances).
In Girl Genius, Gilgamesh and Tarvek became close friends while growing up on Castle Wulfenbach. Their bond is ruined when Tarvek gets sent home for spying, after being told on by Gil- when in fact Gil was his partner in crime, and the secret they were after was the truth of Gil's origins. In the present day, they vie for Agatha's affections. Gil views Tarvek as a "weasel" and an ineffectual dandy; Tarvek, for his part, sees Gil as a libertine cad.
Mr. Blank and Mr. Black in Sam and Fuzzy used to be the two best Blankfaces of the Ninja Mafia until Sam (unwittingly) caused its downfall. Blank stayed loyal, Black decided to use his newfound freedom to sell his skills on the open market and tries using his successes to convince Blank to follow his example. He fails. Fatally.
In The Gamers Alliance, Vaetris and Jahi were once prostitutes in the Demon Realm and close friends, but things changed when they were abused too much and Vaetris's ambition to change their living conditions turned her to the path of conquest, bloodshed and manipulation whereas Jahi chose to nurture her young instead, which set the two on different paths. Ronove and Nesa became friends while the former was amnesiac but once Ronove regained his memories of being a demon lord, he took back his position in the demon hierarchy and ultimately betrayed his friends, Nesa included. However, both cases are more complex and grey than that and have shades of Friendly Enemy because neither Vaetris nor Ronove act in a truly villainous way and they do seem to care for their former friends somewhat whenever they're dealing with them although in both cases manipulation is also involved.
In Noob, Arthéon mentions that his former guildmates are snubbing ever since he got his high-level avatar banned for Real Money Trade. Saphir was okay speaking to him in Season 1 (but not helping him finish the quest needed to get a sword), while Ystos is still friendly to him. Fantöm was explicitly not aswering his e-mails in Season 1 , but is back to speaking terms with him after Season 3 due to circumstances putting them in the same guild.
In Gargoyles this occurs between Macbeth and Demona, as seen in "City of Stone": best of friends when they first fought together against Duncan and won Macbeth his kingdom, things go south when Demona, mistakenly believing that Macbeth was about to betray her and her clan, betrays him first, causing him to lose his kingdom, family, and identity.
Occurs in the second Teenage Mutant Ninja Turtles 'toon between Leonardo and the Shredder's adopted daughter Karai, who in previous seasons had developed a rapport of sorts with him, despite their Feuding Families. When the turtles successfully stop the Shredder's plan to leave Earth to conquer the Utrom homeworld, and end up getting him imprisoned and exiled, Karai takes it as a betrayal, and vows to avenge her father. Later, after Karai destroys the turtles' lair and believes she's killed the other turtles and Splinter, she heads into April O'Neil's shop and asks her to give Leonardo a message. When April asks Karai (whom she's never met before) how she knows the turtle, she responds with the trope name.
Plankton and Mr. Krabs of SpongeBob SquarePants. They used to be close friends but are now mortal enemies because of the Krabby Patty formula.
Avatar: The Last Airbender reveals that Aang's predecessor, Avatar Roku, used to be best friends (with a lot of Ho Yay,) with Firelord Sozin, the man who started the Fire Nation's war for world domination, and committed genocide against the airbenders.
Rainbow Dash and Gilda in "Griffon the Brush Off". They used to be childhood friends, but their friendship is broken off after Dash finds out that the latter has been bullying her other friends behind her back.
Rarity and Sweetie Belle in "Sisterhooves Social", thanks to the latter's poorly-executed attempts to help out with Rarity's house chores. This results in Rarity becoming more and more frustrated with her younger sister, and eventually an argument breaks out where Sweetie Belle calls her big sister out for being ungrateful. The fight ends with the two deciding that neither of them wants the other as a sister anymore.
Twilight Sparkle: I was just trying to- Shining Armor: She's been completely stressed out because it's really important to her that her big day be perfect! Something that obviously wasn't important to you. Now if you'll excuse me, I have to go and comfort my bride. Oh, and you can forget about being my best mare. In fact, if I were you, I wouldn't show up to the wedding at all. Applejack: C'mon, y'all. Let's go check on the princess. (Everypony coldly walks past Twilight. Celestia is the last to leave.) Princess Celestia:You have a lot to think about!
Later a subversion. When Twilight is proven to be right all along, Applejack apologizes for ditching Twilight on everyone's behalf. Twilight holds no grudge.
In Twilight's Kingdom Part 2, seeing the ponies (especially Fluttershy) absolutely broken by Discord's betrayal really punches him in the gut... but he's sided with Tirek, so there's no turning back now... or so it seems.
One of the subplots of My Little Pony Equestria Girls. The Human 5 were friends at one point in the past, but they had drifted apart when Sunset Shimmer sabotaged their friendship, then Twilight and Spike crossed over to fix things.
Jacob and Kane (along with Dr. Hudson, although he's not really a bad guy) in Motorcity. Jacob now fights KaneCo with the Burners and helped design their bots, which gives him some inside knowledge.
Daffy Duck gives Bugs Bunny mad ups in "Porky Pig's Feat." When they get paired up over ten years later, Daffy becomes the Iago to Bugs' Othello.
In Scooby-Doo! Mystery Incorporated, Scooby was on the outs with Shaggy, who he had discovered was romancing Velma, and with Velma in a jealous snit over Shaggy. Fortunately, fences were mended soon after.
The Tiny Toon Adventures episode "Citizen Max" shows Buster and Montana Max used to be the best of friends when they were younger, they shared whatever they had because Max was poor, then his parents won the lottery and Max became a selfish, greedy jerk and cut off his friendship with Buster.
Vercingetorix and Caesar, if the latter is to be believed.
Often found in political discussions and developments. Former associated politicans changed their views or motivations.
This troper being from Germany has to think of Gerhard Schröder (who would become Chancellor of Germany years later) and his fellow social-democratic party (SPD) buddy Oskar Lafontaine who had an intense fight spanning years due to differing opinions.
Pete Doherty and Carl Barât of The Libertines seem to have estranged over the years.
Don Henley and Glenn Frey of The Eagles wrote the title song to The Long Run partially based on their strained friendship and how they were optimistic that they would work it out like they always do. The band (and their friendship) broke up for over a decade a year later.
Before Genghis Khan was Genghis Khan, he was Temüjin, and he was best friends since child hood with boy named Jamukha. Eventually, Jamukha was declared a Khan himself. Temüjin refused to accept this, and the two who had been as brothers went to war with one another, with Temüjin being victorious due to his more progressive methods and tactics, along with Jamukha's forces betraying him. After rewarding the traitors, Temüjin offered the defeated Jamukha a place by his side so that they could resume their friendship, but Jamukha declined with the following speech;
Jamukha: What use is there in my becoming a companion to you? On the contrary, sworn brother, in the black night I would haunt your dreams, in the bright day I would trouble your heart. I would be the louse in your collar, I would become the splinter in your door-panel...as there was room for only one sun in the sky, there was room only for one Mongol lord."
Then he asked to be killed without having his blood spilled. Temujin's soldiers broke his back.
Paris Hilton and Nicole Richie. Big time.
Sigmund Freud and Carl Jung. After a few years as colleagues, Jung tried to convince Freud that focusing purely on the sexual roots of human motivation was too limiting. He believed that the subconscious is not so much the repository of repression as it is the wellspring of creativity. He also promoted the idea of the Archetypal Character, and that many actions are based on patterns that tend to repeat themselves. (Perhaps this makes him the ultimate Trope Codifier of ... well, of tropes.) Freud disagreed with what is now called Jungian psychology because, naturally, he believed that All Psychology Is Freudian.
Friedrich Nietzsche and Richard Wagner. Nietzsche even wrote two books explaining his perspective: The Case of Wagner to mark his break, and Nietzsche contra Wagner to explain how his thoughts on music had been consistent, but his earlier application of them to Wagner had been incorrect.
Shaquille O'Neal and Kobe Bryant
Shaq and Kobe were never friends. At best they tolerated each other for the sake of winning championships.
Harry Houdini and Sir Arthur Conan Doyle were very good friends who bonded over a shared interest of the Occult, Spiritualism to be exact. The two would go around looking for people who claimed to be psychics or mediums or witches, etc, but where Houdini was an Open but heavy Skeptic, who believed everything to be fake until proven otherwise, Doyle tended to believe everything at face value (ironic). The two eventually went different ways after Houdini declared Doyle's wife, who claimed to be a Ghost writer, a fake.
David Letterman and Jay Leno. Leno helped inspire Letterman to try comedy, then Leno became one of Letterman's early supporters. Then Leno was Letterman's most frequent guest during the early years of Late Night, which boosted Leno's profile and led to him becoming Johnny Carson's fill-in host. Then Carson retired and NBC picked Leno to replace Carson, a job that Letterman considered himself the heir-apparent for.
Lil' Kim and Nicki Minaj used to be on good terms, believe it or not. Nicki Minaj used to give a shout out to her in interviews as a inspiration, and there are pictures of them smiling and putting their arms around each other at a concert. Minaj also said she was a die hard fan of her as a kid. Then, for reasons ambiguous, they became enemies and wrote various songs targeted at one another defaming the other, and calling each other very profane words. They still put references to how much the other one sucks in their mix tapes, and are sure to bring the other one up in the interviews even when not asked.
This probably happened to anyone who used to be friends with someone but can no longer be as such due to betrayal, betrayals, general growing apart, personal growth or lack there of or a similar event or EVENTS.
Never mind the friends who just stop hanging out after graduation or leaving a place of often hanging out/being there, like School, Collage, Uni, other educations and all work places.
No longer being in the same city/state/country/school, falling out that way...
Another notable historical example was William Marshal, known for actually keeping to his word in an era of political expediency. He followed Henry II's eldest son, then followed Henry II, even when Richard (the Lionheart) rebelled against his father. The trope comes in due to William tutoring Richard and even being good friends, yet they came face to face during the retreat of King Henry's army. William Marshal, owing to being perhaps the most skillful warrior in Christendom at the time, was able to kill Richard's horse and let the man live.
John F. Kennedy and Richard Nixon were friendly while serving in Congress together. Kennedy reportedly donated money to Nixon's 1950 Senate campaign, and the two retained offices across the hall from each other after Nixon became Vice President. The presidential campaign in 1960 ended their friendship; Nixon felt especially angry that when he was hospitalized, Kennedy neither visited him nor suspended his campaign. For Nixon, this mutated into near-pathological hatred of not only JFK but his brothers as well.
Wil Wheaton and River Phoenix became friends after starring together in Stand by Me, but their friendship fell apart as Phoenix developed drug problems which would sadly end his life.
Vladimir Lenin and Josef Stalin were friends thanks to their beliefs, but as Stalin became more violent, Lenin wrote to Trotsky to ask him to unite to try and get rid of Stalin, who Lenin thought was getting out of control.
What for Lenin was crossing the line twice was that Stalin became angry at Nadezha Krupskaya, Lenin's wife, for updating Lenin in party-related manners when the doctors told him to rest. Lenin was receiving daily fake Pravda numbers with good news (the HBO movie Stalin portrays this incident), and Nadezha realized that Stalin was trying to isolate Lenin. Stalin confronted Nadezha and insulted her, calling her a "whore", which reallymade Lenin upset and made a chain reaction that led to his secret block with Trotsky and his final Testament.
Boxing superstar Floyd Mayweather Jr. and popular Rapper 50 Cent. They used to be seen everywhere together, but had a falling out in 2011, which resulted in a brief twitter feud.
Before the infamous East Coast Vs. West Coast Hip Hop war in the mid-90s, late rappers Tupac Shakur and Notorious BIG were good friends and even appeared on some television interviews together. Tupac helped Biggie Smalls get into the business and even helped him with his lyrical style that he would later became famous for. All this changed after Tupac was shot five times and robbed while at Quad Recording Studios. He survived the shooting and blamed Biggie Smalls and Sean Puffy Combs (P Diddy), who were also there at the time of the shooting. Being an artist signed to Bad Boy Records, P Diddy's label, Biggie Smalls denied having anything to do with the shooting and defended his boss. Tupac would then start doing interviews dissing Biggie Smalls. Biggie Smalls mostly ignored the comments by Tupac and would change the subject whenever asked about it during an interview. Meanwhile, he released a hit rap song called, "Who Shot Ya?" Many fans immediately thought it was a Tupac diss and him admitting that he was responsible. Biggie Smalls, however, denied it and claimed it was just another rap song. Tupac responded by releasing "Hit Em Up" his famous Take That where he admitted to having sex with popular R&B artist Faith Evans, who at the time, was also Biggie Smalls wife. Biggie Smalls was shocked when he heard this and soon divorced her. And it would only get worse.
Luis Buñuel and Salvador Dali had a very nasty falling out during the production of L'Age D'Or, due to Buñuel's Communist sympathies and Dali's support for aristocrats and, later, Spanish dictator Generalissimo Francisco Franco. They never resolved their issues either.
Butch Hartman and Steve Marmel. The two were partners and the closest of friends during the pre-2008 episodes of The Fairly OddParents and the first two seasons of Danny Phantom. The two had a falling out over the third season of the latter (Marmel wanted the show to take a more serious route and supported Danny's relationship with Valerie Gray while Hartman was against it and insistent on Danny ending up with Sam Manson) which resulted in two ending their partnership and friendship.
Frank Zappa and Captain Beefheart. These high school friends got along fine until the failed commercial success of Beefheart's album Trout Mask Replica (1969), which was produced by Zappa. Beefheart blamed Zappa and for about six years they had a fall-out. After Beefheart's career financially faltered, Zappa took him on tour in 1975-1976 and recorded the album Bongo Fury with him, to help him out. Beefheart also performed mouth harmonica on Zappa's One Size Fits All and Zoot Allures on the pseudonym Bloodshot Rollin' Red. Unfortunately they had another fall-out soon after, because both were constantly trying to outdo each other in experimental weirdness. Only in the early 1990s, when Zappa was already ill with cancer, did the two friends finally make up.
Zappa also had a fall-out with Wild Man Fischer, a local nutcase whose debut album, An Evening With Wild Man Fischer (1969) was produced by Zappa. One time Fischer threw a bottle at Zappa's infant daughter. He missed, but Zappa was furious and threw him out immediately. Fischer made matters worse by openly blaming Zappa for the commercially low sales of An Evening With Wild Man Fischer. They never reconciled. To this day An Evening With Wild Man Fischer has never been re-released again, not even on CD. Fischer died a poor man in 2011.