Anne of Avonlea: Anne is pursued by both Charlie Sloane and Gilbert Bylthe. It is hinted that she was in denial of a her attraction towards Gilbert all along, and later that she loves both Roy and Gilbert in Anne of the Island.
In Beautiful Losers, the narrator is sleeping with F. while married to his wife Edith, but F. is also secretly sleeping with Edith. It's the sort of situation that should lead to a Marry Them All situation, but never does for some reason.
Bedlams Bard series by Mercedes Lackey: Eric, Beth, and Kory, the main characters of the first two books are in one of these. Definitely sexual in this case; Kory is bi, Beth is attracted to both guys, and Eric spends the first book struggling with the idea that he is bi (although he doesn't struggle very hard). Results in a happy, magical (literally) threesome, at least for a while.
The Belgariad features a somewhat... complicated example between Mandorallen, Nerina (the Baroness of Vo Ebor) and the (considerably older) Baron of Vo Ebor. Mandorallen is hopelessly in love with Nerina, Nerina is in love with him, and the Baron is (accurately) aware not only of the love but also that both are too noble to do anything, given Nerina is married to him and Mandorallen sees him as a mentor and father figure — the Baron's solution is to try to invoke Death of the Hypotenuse on himself by picking up dangerous hobbies like dragon-hunting, warfare and duelling people who badmouth his wife and protege. Apparently generations of Mimbrate maidens have wept at the tragic nobility of it all. The Baron dies early in The Malloreon of wounds inflicted towards the end of The Belgariad, clearing the way warfor Mandorallen and Nerina to marry once Belgarion gets everyone involved to stop being so wrapped up in the mess. At swordpoint.
In Tom Clancy's The Cardinal of the Kremlin, a woman (A) is desperately in love with another woman (B), who is in a committed relationship and engaged to a geeky young male major (C) responsible for an American secret weapons program. When circumstances separate B from C, in no small part due to A's treasonous efforts, B is devastated and A tries to show B how much she loves her. The love remains unrequited, which shatters A so badly that she gives up everything she knows under interrogation.
In Richard Ellis Preston Jr.'s Chronicles of the Pneumatic Zeppelin, both Max and Sabrina are in love with Romulus — who, in spite of their all being older children when adopted, thinks it Brother–Sister Incest and feels guilty about it.
Children Of Eden: Both Lark and Lachlan love Rowan, but Rowan doesn't know who she loves. She ends up deciding to just say she loves both of them, as she feels like any other answer will make them both upset.
The Chronicles of Dorsa: Linna has feelings for Megs, who loves Akella and doesn't think of her that way.
In The Comfortable Courtesan, Josiah Ferraby is initially one of Clorinda's clients with his wife Eliza's acquiescence, but Clorinda and Eliza become friends, and then start sleeping together as well, leading to a long-lasting and equally-balanced three-way relationship.
Chloe has feelings for both Simon and Derek, and both of them have feelings for her. Simon and Derek are brothers. Awkward. She's confused about her own feelings, and barely realizes that she has more-than-friendly feelings for Derek. In the end, it turns out that she does like Simon, but just as a friend. She's honestly in love with Derek, even if it takes both of them a bit of time to work things out and get together. Some completely understandable angst ensues between Simon realizing that Chloe likes Derek, and Chloe and Derek finally figuring out that their feelings are mutual, but everyone involved is actually mature about it, completely free of pettiness, and no one resents anyone because they all act like rational people.
In the beginning, it looked like the triangle would be a rather generic Main Character Girl vs. Alpha Bitch for The Nice Guy between Chloe, Simon, and Tori, though this was resolved fairly early when Tori’s mother warned her to stay away from Simon practically under threat of death. Tori then tells Chloe that Simon is all hers right before hitting her in the head with a brick and hog-tying her as revenge for making her already crappy life even MORE miserable. Though, she gets over her crush after being forced to spend a few days alone with him. And then later on it turns out they’re half-siblings, which explains why Mrs. Enright was so adamant about Tori staying away from him. Cue awkward music!
Also played with in The Reckoning when Tori makes a comment about Derek actually not looking so bad, though this was more a casual observation and a chance to tease Chloe than anything serious. Doesn’t stop Chloe from getting mad, though.
The Day of the Locust features two significant examples, both with aspiring but untalented actress Faye Greener at the centre.
Much of the plot is driven by protagonist Tod Hackett and Deuteragonist Homer Simpson's contrasting forms of unrequited love for Faye. After she rejects him, Tod's love for Faye becomes an obsession with possessing and destroying her, and most of his actions toward her are motivated by his own selfish desires for her than out of any concern for her. Homer is the opposite; Faye is equally uninterested in a romantic relationship with him, but he happily soaks up her abuse and caters to her every whim in a doomed bid to make her happy. Tod and Homer's own friendship starts to break down thanks to their divergent attitudes toward Faye.
Faye is overtly romantically interested in dim-witted cowboy Earle Shoop, but flirts with, and eventually sleeps with, his friend Miguel to make him jealous. In Chapter 14, Earle attacks Miguel with a club when he dances with Faye at their campsite, and in Chapter 24, Homer tells Tod that after Earle found Miguel and Faye in bed together, the two men got into a fistfight, and the next morning, all three of them had moved out of his house.
Taylor Anderson plays with love triangles as sub-plots in his Destroyermen series.
The first one introduced involving Chack, Selass, and Saak-Fas (eventually a fourth party, Safir, gets thrown into the mix). Chack initially loves Selass, but Selass puts him down and chooses Saak-Fas, another suitor. After Saak-Fas is lost in battle, Selass refocuses her love on Chack. Oddly enough, this same battle is what makes Chack forget about Selass and when Saak-Fas is found alive as a prisoner of war/rations for the Grik, Selass is unable to mate with Chack for a while. Once Chack meets Safir, Selass becomes the unlucky suitor instead of Chack.
Is somewhat downplayed and possibly subverted with one of the human Destroyermen, Dennis Silva. Silva attracts the attention of the human nurse Pam, and Lemurian warrior Risa. His solution to this is that he has relationships with BOTH of them simultaneously, as he loves them equally, and both females seem to consent with this.
In the Brazilian book The Devil to Pay in the Backlands, Otacília loves Riobaldo, who likes her and could even love her back if he wasn't already in love with Diadorim, who seems to love him too, but he has his own reasons - besides being both male - to stay quiet.
Diary of a Wimpy Kid: The Third Wheel: Greg likes Abigail, but Abigail likes Rowley. Greg loses.
In the Dragonlance Chronicles Tanis Half-Elven is initially torn between Laurana, a heroic, kind-hearted elven princess, and Kitiara, a sultry, cruel human warlord, but eventually decides it is Laurana he loves.
Enoch Arden: Enoch and Philip both love Annie; all three are also childhood friends. Annie first marries Enoch and then, after he is lost at sea and presumed dead, she marries Philip.
In the final book of The Faerie Queene, Calidore falls in love with Pastorella, but she's already being courted by Coridon. Coridon is intensely jealous as Pastorella falls for Calidore more and more, but Calidore bears no ill will in return.
Seen in Paul Kidd's Talking Animal novel The Fangs of K'aath when one of the three main protagonists, Raschid, marries BOTH of the others, Sandhri and Yariim, who have also been feeling a growing attraction towards each other.
Fear of Flying: Isadora and her husband Bennett go to a conference in Germany, where Isadora starts having an affair with Adrian. It's strongly hinted that Adrian is interested in Bennett as well—the narrative comments on it several times—and at one point, it's implied that the two men slept together.
Fight Club features the quote "Tyler wanted marla, marla wanted me and I wanted Tyler". Although things get skewed in the third act as certain things unravel.
A rather twisted variation shows up, with Gauron attracted to Sousuke, who has a mutual Bodyguard Crush with Kaname. Gauron is a creepy bastard who is in love with Sousuke's carnage and is quite the yandere to boot. Sousuke, for his part, wants nothing to do with this guy, and would much prefer he die or leave him the hell alone.
A less disturbing one by the end of The Second Raid: Sousuke appears to have finally embraced his feelings for Kaname, while patching things up with, but not necessarily entering into a relationship with, Tessa.
Later still in the series we have Tessa's evil older brother Leonard, who keeps trying to win over Kaname despite her making it clear at every given opportunity that she utterly despises him and is in love with Sousuke.
The Golden Oecumene: Phaethon is in love with his wife Daphne Prime, who drowned herself in a simulated dream, and emancipated a partial personality, Daphne Tercuis, whom she thought would be better suited to Phaethon, and who is madly in love with him. Owing to Laser-Guided Amnesia, neither Phaethon nor Daphne Tercuis know this at the opening, and because Daphne Tercius derives from Daphne Prime, she had most of her memories, and Phaethon confuses the two of them. Eventually he realizes that most of his fondest memories of Daphne are of Daphne Tercius and asks her to marry him in her own right.
Austin, from Grasshopper Jungle is in love with both his girlfriend Shann and his (male) best friend Robby, and both of them like him back.
Cry it out loud for The Great Gatsby, Daisy is married to Tom Buchanan, Jay Gatsby is Daisy's ex-boyfriend who's willing to do anything to get Daisy to love him again. And Daisy actually falls in love with him again, even though she still loves Tom. It doesn't end well.
A Ron/Hermione/Krum triangle breaks out at the Yule Ball.
Harry has a crush on minor character Cho Chang, who is not averse to it but gets asked out by Cedric Diggory first. Cedric is murdered by Peter Pettigrew on Voldemort's orders during the climax, while Harry and Cho have a falling-out over her friend informing on Dumbledore's Army to Umbridge in Order of the Phoenix.
Harry Potter and the Deathly Hallows reveals the existence of a Snape/Lily/James triangle when Harry rewinds the lifetime memories of the deceased teacher via the Pensieve. Snape and Lily Potter nee Evans were childhood sweethearts, but fell out when Snape became involved with the far-right gangs at Hogwarts that birthed the Death Eaters; she married his Arch-Enemy James Potter. Snape never really got over her.
Haruhi Suzumiya: In Haruhi's student film, "The Adventures of Mikuru Asahina", there is some sort of love triangle between Mikuru, Yuki Nagato, and Itsuki Koizumi, to the point where the two girls transfer into Itsuki's school. However, this was just a case of Haruhi losing sight of the characters' actual conception: Mikuru is a Magical Girl from the future, Yuki is a Human AlienDark Magical Girl, and Itsuki is the Living MacGuffin whom the former two battle over.
Kyon: Yuki and Mikuru's story of battling has now turned into a heated romantic comedy, or rather nothing more than a love triangle.
In Haruka Nogizaka's Secret, Shiina is in love with Yuuto, who is with Haruka. At least she gets to spend one episode largely with him in episode 7 of Season 2.
In Arrow's Fall of the Heralds of Valdemar series, this is what Dirk thinks is occurring in the Love Triangle between himself, Kris, and Talia. Of course, he and Talia are really lifebonded but are in denial about it, while Kris and Talia did in fact have an affair that is now over. Add in a healthy dose of Poor Communication Kills and Drowning My Sorrows, and it takes Kris' actual death, Talia's near-death, and something akin to divine intervention to sort things out.
The Heroes of Olympus, has Piper, who likes amnesiac Jason, who also likes her but is conflicted because he has just met Piper and he vaguely remembers another girl from home, named Reyna, who is implied to have feelings for him but needs someone to replace him with in the role of praetor, and promptly asks Percy, also informing him that the position would require a certain closeness, while Annabeth, Percy's girlfriend, searches for him all over the country. In the meantime, Frank gets involved with Hazel, who had a boyfriend back in the 1940's who appears to be related by blood to present-day Leo, since they look exactly the same.
A Home At The End Of The World (also a film): Jonathan loves Bobby and Bobby clearly reciprocates to some degree, but is also in a sexual relationship with Clare, who loves Jonathan platonically, as he does her. For a time they all live together and raise Clare's baby, who is presumably Bobby's.
Honor Harrington: Honor falls in love with her longtime mentor Admiral Hamish Alexander, Earl White Haven. They initially try to avoid it because he's married, but Emily, who was paralyzed in an accident decades earlier, quickly gives her approval when she learns of the attraction. Fortunately, polygamy is legal on Manticore (and even if it wasn't, Honor has dual citizenship on Grayson where polygyny is widespread).
The Host (2008) features one In two bodies! Melanie and Jared were together before Wanda took over her body and then Wanda and Ian fall in love. It's ultimately resolved when Melanie gets her body back and is free to be with Jared, while Wanda gets a new body and is free to be with Ian.
The Hunger Games: There is romantic tension between Katniss and Gale and Peeta, though the books don't focus on it very much.
The Iliad may be the Ur-Example. The Trojan War was a consequence of the Love Triangle between Helen, Paris, and Menelaus: Helen was married to Menelaus but Aphrodite makes her fall in love with Paris as payment for him giving her Eris's golden apple. Then there's the whole problem caused by the triangle between Achilles, Briseis, and Agamemnon.
Will—>Tessa<—Jem in The Infernal Devices. Jessamine lampshades it in The Clockwork Prince.
Jessamine, mocking Tessa: Oh, I must choose between Will and Jem! Whatever shall I do?
The Kane Chronicles feature Sadie, having to pick between Walt and Anubis. Anubis is a Egyptian boy-god that the other gods forbid Sadie to go near and Walt is dying because of a curse. The triangle is solved by Walt hosting Anubis, thereby keeping Walt alive and letting Sadie near Anubis, as he's not in his godly form. Yes, the triangle is solved by the two love interests sharing the same body.
In Stephanie Burgis's Kat, Incorrigible: A Tangle of Magicks, Kat realizes with a shock — as Lady Fortherington complains to Papa about how he had refused to listen to her warnings about Kat's mother— that she was jealous, having lost out in a triangle.
Kaze no Stigma: Ren with his two best friends (a guy and a girl), and Kazuma with Ayano and Katherine.
The Thai Narrative PoemKhun Chang Khun Phaen, has Khun Chang in love with Wanthong, who is already a fiancée of Khun Phaen, and Khun Phaen is The Casanova who practically loves every beautiful girl he comes across, including Wanthong. Due to the multiple events of kidnapping and husband switching, Wanthong develops feelings for both. Tragically, Wanthong ends up getting beheaded for not be able to decide who she really wants to live with.
In the earlier part of Kushiel's Dart, Phèdre and Alcuin are both completely in love with their Sexy Mentor Delaunay. Delaunay is Oblivious to Love and has no idea until he's told—he thinks they see him as a Parental Substitute. Delaunay consummates with Alcuin, but they're both killed by The Conspiracy not long after.
Legendborn: Bree and Nick have clear and mutual romantic interest in each other, but as they grow to know and understand each other, Bree finds herself attracted to Sel, and he calls her "cariad" meaning "love".
Several of these appear in Life and Death: Twilight Reimagined. All of them are set around Beau, who has the attention of several girls, to the frustration of the boys who are interested in these girls. Beau tries to solve these by setting up the girls with the boys who like them, like convincing McKayla that Jeremy likes her, or publicly blaming Taylor of Operation: Jealousy. Eventually he becomes a couple with Edythe, turning it into an Unwanted Harem.
Jack Campbell's The Lost Fleet at least for the first four books. While its clear that Desjani is head over heels for John Geary, Geary is already in a relationship with Rione, which gets complicated when they find out Rione's husband may not be dead. And they're all on the same ship.
One of Heinrich Heine's most-quoted poems, No. XXXIX of the Lyrisches Intermezzo, describes a situation like this: A young man loves a young woman, she loves a different man who loves and marries someone else entirely. The young woman then marries somebody who happens to cross her path, leaving the first young man distraught:
Das ist eine alte Geschichte, Doch bleibt sie immer neu; Und wem sie just passieret, Dem bricht das Herz entzwei.Trans.That is an old story, but it always stays new; and it breaks the heart of anyone to whom it happens right now.
Théophile Gautier's 1835 novel Mademoiselle De Maupin is about a poet named D'Albert and his mistress Princess Rosette who are both Sweet on Polly Oliver for a charming cavalier who goes by Théodore. In the end, Théodore has a one-night stand with each of them separately, but that's the last either sees of her.
Magician by Raymond E. Feist has the Pug/Carline/Roland triangle. Pug never tries to commit and Carline angsts over him for a large chunk of reasons for various reasons.
In The Maze Runner, while Thomas’s original love interest is Teresa, he ends up growing closer to Brenda in The Scorch Trialsafter being separated from Teresa for an extended period of time, and finding out that she had betrayed him. He eventually ends up with Brenda, partially due to him never forgiving Teresa for what she had done and partially because of the girl’s sudden death at the end of The Death Cure.
In Memoirs of a Geisha Nobu is in love with Chiyo/Sayuri, who has been in love with the Chairman for decadesand the Chairman loved her all along, and was the reason she was able to become a geisha in the first place.
Midnight's Children: During Saleem's childhood he develops a crush on Evelyn Lilith Burns (an American girl who moves into his gated community), but she develops a crush on his friend Sonny, who in turn is enamored with Saleem's sister the Brass Monkey. The Brass Monkey doesn't love anyone, and reacts violently to shows of affection.
To save time, I shall place all of us in the same row at the Metro cinema; Robert Taylor is mirrored in our eyes as we sit in flickering trances — and also in symbolic sequence: Saleem Sinai is sitting-next-to-and-in-love-with Evie Burns who is sitting-next-to-and-in-love-with Sonny Ibrahim who is sitting-next-to-and-in-love-with the Brass Monkey who is sitting next to the aisle and feeling starving hungry.
Eponine loves Marius, who loves Cosette, who (eventually) loves him back after a bit of trepidation.
Implied with Joly and Bossuet, who "shared everything, even, to some extent, Musichetta [Joly's unseen mistress]." This is often interpreted as them being in a polyamorous relationship, although it could be that Musichetta is only involved with them separately.
Monster of the Month Club: Rilla has a not-so-secret crush on her friend Joshua Banks. So does their classmate Tina Welter, which is one of the reasons she and Rilla don't get along. Josh, for his part, is largely content to just be friends with them both.
In the Mr. and Mrs. Darcy Mysteries Georgiana finds herself subjected to one when two men start vying for her attention.
My Sister, the Serial Killer: Korede, the narrator, loves Tade, the doctor she works with, but he does not return her feelings. Instead, he is infatuated with her sister Ayoola (the serial killer), who likes him too.
The Mysteries of Pittsburgh has main character Art Bechenstein falling for both Phlox and his friend Arthur in a bisexual variant.
Shows up in the hints of the last book in the Night World series. Soul mates exist, and are usually A<—>B-type relationships. Then a main character sees the silver thread associated with soulmate bonds going from her to two guys...
Nina Tanleven: In The Ghost in the Third Row, Lily Larkin was in one with two members of her acting troupe - Edward Parker and Andrew Heron. When she chose Edward, Andrew was furious and killed her.
Pearl: Pearl develops a romantic relationship with both Reuben and David without knowing that the two men have a had a decades-long, extremely painful history with one another before Pearl's arrival. David has only recently forgiven Reuben, while Reuben, out of guilt, is now highly protective of David. Pearl realizes that telling either that they are now romantic rivals might push both over the edge.
Percy Jackson and the Olympians, where hero-turned-villain Luke is implied to have had feelings for the seemingly deceased Thalia, and is fancied by Annabeth, who also slowly developed a conflicting crush on main protagonist Percy, who returns the crush but also has mixed feelings for Rachel, who is attracted to Percy but in the end figures out that she is attracted to him jut because he is her key to the mythological world, while Annabeth figures out that she loves Luke as a brother, conveniently after the latter performs a Heroic Sacrifice.
The Phantom of the Opera: Raoul and Christine are recently reunited childhood friends who fall for each other. Erik, a.k.a. the Phantom, is Christine's music teacher and is also in love with her.
In Please Don't Tell My Parents I'm a Supervillain, Penny likes Ray and Ray likes Claire. Or at least so she believes. In the end, it turns out Ray likes her back and she was just totally oblivious.
Jun'ichiro Tanizaki's novel Quicksand 1931, which has at least three film adaptations and furthermore inspired the film The Berlin Affair by Liliana Cavani. Depraved Bisexual misfit beauty Mitsuko hooks up with bored housewife Sonoko Kakiuchi. Sonoko's hubby wants a part of the action, and the couple grow morbidly jealous of each other. Mitsuko drugs the two so that they can only have sex with her but not with each other. The affair ends with a Suicide Pact wherein only Sonoko, betrayed by the other two, lives to tell the tale.
Oliver and Nanao have had a strong romantic tension since early in volume 1 and admit to the attraction in volume 4 (their romance is a slow-burning one). Their friend and Nanao's roommate Katie also has an unrequited crush on Oliver, and Oliver's AMAB Sex Shifter roommate Pete also is starting to act like a bit of a Tsundere towards him. Nanao also has her own unwanted suitors, notably Tullio Rossi, who makes more than a few passes at her without success.
Posthumous Character Chloe Halford had multiple pursuers while she attended Kimberly. Theodore McFarlane recalls having fought a duel with Edgar Groves over their relationships with her, and Esmeralda, the academy headmistress in the present day, was also in love with her. She ultimately chose Edgar, and Oliver Horn was the result.
The Ripple System: Frank thinks he's in one with Darling (the love of his life) and Ned (his greatest enemy). In reality, Darling just thinks he's funny, and Ned finds it hilarious to antagonize him. Darling suggests playing it up a little bit. It's implied that Darling might have real feelings for Ned, but Ned doesn't notice.
The School for Good and Evil features a triangle between Sophie, Agatha, and Tedros (son of King Arthur). Sophie loves Tedros, and Tedros loves Sophie, but in all of their lessons on picking Good from Evil, keeps picking Agatha. Tedros eventually comes to feel love for Agatha, who starts to feel something for him, but is loyal to her friend Sophie and keeps trying to mend their relationship. Sophie ends up a full-fledged witch, and then goes to various lengths to win/kill Tedros AND Agatha. Sophie eventually takes a death blow meant for Agatha, and then makes a Dying Declaration of Love to her ( She got better )
Seraphina: Lucian and Glisselda have an Arranged Marriage necessary to ensure the stability of their country, but are Like Brother and Sister. Lucian and Seraphina fall in love and eventually begin an affair. Glisselda also has feelings for Seraphina, which she realizes are unrequited, but decides to support Lucian and Seraphina. While the details are left ambigious, they seem to end in a stable polyamorous relationship, and the companion novel implies that Glisselda will raise Seraphina and Lucian's child as her own child by Lucian.
"The Rangers Three" in The Shadow of the Avatar trilogy go somewhere here. Sharantyr just does not want to abandon either and focus her attention on only one; Belkram and Itharr know this, but stay as the Vitriolic Best Buds they were.
William Shakespeare's Sonnets. The first 126 sonnets are full of Ho Yay and written to the Fair Youth. The following 28 are written to the Dark Lady. Sonnet 144 brings the triangle full circle by implying that the Fair Youth and Dark Lady are also lovers. Of course, there is jealousy and angst, at least on the narrator's side of things, and it's not clear whether he is still involved with either at that point.
In Shakugan no Shana, Shana and Yuji Sakai are the main couple. Kazumi Yoshida crushes on Yuji.
Lois McMaster Bujold's The Sharing Knife: Utau and Razi appear to be a gay couple when the unworldly protagonist first encounters them; then she finds out that as well as having a sexual relationship themselves, they're married to the same woman. In their culture, birth rates are low and marriages are often dissolved if no child is conceived, to give at least one partner a chance to have children with someone else. When Utau and Sarri didn't conceive, instead of splitting up they brought a third party into the marriage (and had a little girl). It's clear in later books that polyamory of this kind is unusual and not everyone approves.
In Shanghai Girls, sisters Pearl and May both want Z.G Li. In Pearl's eyes, she is Z.G.'s true love, but that is not the case. Z.G. and May have a relationship and May ends up getting pregnant. In the sequel Dreams of Joy, there is a partially platonic one going on, with both Pearl and her daughter Joy actually May's child with Z.G. both wanting love and affection from him.
Sisterhood Series by Fern Michaels: By the book Deja Vu, one has clearly developed between Maggie Spritzer, Ted Robinson, and Abner Tookus. Maggie loves them both, but in different ways. She was engaged to be married to Ted. However, she calls off the engagement to Ted and says that the two should just be friends. She tells Abner how she feels about him, but he does not forgive her mistreatment of him, and their relationship comes to an end. The book Home Free has her hooking up with Augustus "Gus" Sullivan, and apparently Abner finally forgives Maggie. Whew!
In The Sky Is Everywhere, Lennie is in love with Joe, but also has "physical relations" with her dead sister's boyfriend (and fiancé) Toby. She picks Joe.
Before the series's start (this is recounted in flashbacks), Catelyn Tully was in love with Brandon Stark, while her father's foster son Petyr "Littlefinger" Baelish loved Catelyn (additionally, Catelyn's younger sister Lysa was in love with Petyr but he never reciprocated her feelings). So when Brandon came to claim Catelyn's hand, Petyr dared the much older, vastly stronger and vastly more skilled Brandon to a sword fight over Catelyn. Petyr was nearly slain and developed a seriously unhealthy obsession with Catelyn (who, by the way, had to marry Brandon's brother Ned after Brandon died). In A Game of Thrones, Petyr manipulates events to contrive ways for him and Catelyn together, tricking Lysa into murdering her husband Jon Arryn and then Ned into a failed palace coup that gets him executed. When he fails, he goes after Catelyn's young teenage daughter Sansa.
And there's another major love triangle before the series' start: Robert Baratheon/Lyanna Stark/Rhaegar Targaryen. Robert was in love with Lyanna (though it can be alternately interpreted as an aspect of his bromance with her brother Ned) and betrothed to her. She was abducted by Rhaegar Targaryen, who had named Lyanna his "Queen of Love and Beauty" at an earlier tourney despite his marriage to Elia Martell. It's implied that Lyanna's abduction was the final straw for Robert, who started a war against the ruling Targaryen dynasty and personally killed Rhaegar during one of the battles.
A third: Robert Baratheon/Cersei Lannister/Jaime Lannister. Cersei and Jaime had been having sex since they were twelve, but it stopped when Cersei was betrothed to Robert Baratheon. Despite her original infatuation with Rhaegar Targaryen, Cersei was the happiest woman in the Seven Kingdoms marrying Robert, but Robert was still too heartbroken over the death of his original betrothed (Lyanna Stark), causing Cersei to seek solace in rekindling the relationship with her brother. As a result, all three of Robert and Cersei's children are actually fathered by Jaime.
The Courtship of Princess Leia: Han and Leia have been a couple for four years by the time of this novel, but then Isolder Chume, Crown Prince of Hapes, makes a State Visit to Coruscant and proposes a marriage alliance which would help the New Republic greatly. Leia also becomes attracted to him, and legitimately feels torn between him and Han. This continues throughout much of the book, until Isolder falls for another woman, Teneniel Djo, and Leia chooses Han, marrying him at the end.
I, Jedi: Corran Horn is married to Mirax Terrik, who went missing on a mission at the start of the book, and under his "Jenos Idanian" cover identity he crafts a story of a forbidden love affair between him and an heiress to a shipping line. Pirate queen Leonia Tavira, the primary antagonist of the book, develops a Villainous Crush and decides to make him her newest boytoy, not caring about his other lover. Corran considers taking her up on it, briefly trying to rationalize it as a way to make his cover more effective, but then rejects the idea as a dark side-fueled impulse of male pride and chooses instead to accelerate his plans to break up her pirate alliance.
Words of Radiance: One nearly forms around Shallan between Adolin and Kaladin, though Kaladin consciously attempts to defy the attraction once he recognizes it. It helps that by the time Kaladin realizes he's attracted to Shallan, he's also friends with Adolin, and decides it would be best to leave them alone. This gets more complicated in Oathbringer, when Shallan's Lightweaving is causing her to create numerous Split Personalities that have their own opinions on the matter. Prim and proper Brightness Radiant doesn't like Kaladin's rough nature, and wants to hold to the implied oaths she has made with Adolin. Street-wise Veil, on the other hand, finds Adolin boring and much prefers Kaladin's wit and strength. Shallan herself doesn't know what she wants.
Strawberry Panic! centers on two love triangles. Tamao crushes on Nagisa, who is in a relationship with Shizuma. Yaya crushes on Hikari, who is with Amane.
The final chapters of The Tale of Genji involve such a triangle. Ukifune is having affairs with both Prince Niou and Lord Kaoru and it totally isn't her fault; Niou got into her hakama by pretending to be Kaoru, her accepted lover.
In Tales of Kolmar, Vilkas, Will, and Aral are all friends. Aral has an obvious crush on Vilkas, who is aware of it but doesn't want her, while Will pines after Aral, who has no idea. When Aral gives Vilkas her Anguished Declaration of Love it's seen as a betrayal to everyone; when Will gives Aral his declaration it's seen as sweet and romantic.
Tantei Team KZ Jiken Note. By the egg burger arc (fourth in novels, second in anime), Aya may have developed feelings for Wakatake and Sunahara. The problem is Wakatake is occasionally a bit of a jerk to her, while Sunahara has a bad reputation.
Turin is Oblivious to Love, he thinks Finduilas is just his friend and his other good friend Gwindor is unhappy with him for political reasons. Finduilas is devastated that she's fallen out of love with Gwindor and into love with Turin but cannot help herself. Gwindor just wants Finduilas to be happy but doesn't see how Turin can ever be good for her (he's right).
Brandir, Niënor, and Túrin are a tragic example. Brandir falls in love with an amnesiac Niënor under the name Niniel, but she marries Túrin, who is actually her brother. It doesn't end well.
The Lord of the Rings: Éowyn develops a crush on Aragorn, but Aragorn has been in love with Arwen about twice as long as Éowyn has been alive. This one is resolved via Pair the Spares: Éowyn gets over her crush on Aragorn, then falls in love with Faramir in The Return of the King and both couples finish the series Happily Married.
Beren and Lúthien: Lúthien Tinúviel famously gave up her immortality to have her mortal lover Beren resurrected by the Valar. She was at one point also pursued by Celegorm, who captured her and tried to forcibly marry her but she escaped.
The Fall of Gondolin: Maeglin lusts after his cousin Idril, but she despises him. She marries Tuor, while Maeglin's jealous drives him to evil.
Toradora!: This is a very strange twist of Matchmaker Crush. Taiga is trying to set up Ryuuji (who starts to take care of her) with Minori (who is Taiga's best and initially only friend). Taiga develops an emotional dependence on Ryuuji, who develops feelings as well. It turns out that Minori already had a crush on Ryuuji, but also had strong feelings for Taiga. Taiga remains good friends, but doesn't quite reciprocate Minori's feelings. Since the Official Couple is actually the title of the show/novels, bummer for Minori. Since everyone in this triangle is too nice to betray anyone, this draws out for a while.
Trapped in a Dating Sim: The World of Otome Games is Tough for Mobs: The series is set up to look like a standard Harem Series with Angie and Livia both becoming attracted to Leon. Volume 3 turns it on its head: Angie and Livia have also fallen in love with each other, to the point where an airship that runs on The Power of Love can be run by them alone. The volume ends with them getting officially engaged to Leon (Angie, a duke's daughter, as his official wife, and commonborn Livia as The Mistress), and in volume 5 they're shown kissing while Leon is elsewhere.
Some versions of the Tristan and Iseult story portray the love triangle as: Isolde is married to Mark but in love with Tristan, who is in love with her, but is also loyal to Mark, who is his uncle.
The Twilight Saga has Jacob and Edward both after Bella, which crosses the rivalry between Bella's love interests with Fur Against Fang, since Jacob is a skinchanger and Edward is a vampire. Bella marries Edward in book four, and eventually this is "fixed" when Jacob imprints on Bella and Edward's infant daughter.
In Vampire Academy, Dimitri and Rose are in love, but worry that their relationship will get in the way of their mutual duty to protect Lissa.
Vanishing Acts: Delia is liked by both Eric and Fitz. Delia and Eric are engaged, but Fitz and Eric also are attracted to each other. Fitz eventually gets Delia.
Stormfur was also sweet on Squirrelflight for a while in The New Prophecy, but later fell for Brook.
The Prophecies Begin has Spottedleaf and Firestar, who liked each other in the beginning, but she died and promptly began stalking him from above. He then fell in love with Sandstorm, although for a while she wasn't so sure he wasn't still in love with Spottedleaf. And he somehow managed not to realize that he and Cinderpelt weren't Just Friends.
Throughout The New Prophecy to The Power of Three we have the Crowfeather/Leafpool/Feathertail/Nightcloud triangle. Crowfeather fell for Feathertail, who then promptly died, and later ran off with Leafpool because they could never be together because of the boundaries between their Clans, but eventually returned. To prove his loyalty, he hooked up with a cat from his own Clan, Nightcloud, and a kit with her. It was later revealed that Leafpool actually had Crowfeather's kits and was forced to give them up to her sister at first or risk punishment. When this was revealed, he rejected her completely and declared that his mate was Nightcloud and his kit was Breezepelt.
In The Power of Three, Lionblaze used to love Heathertail, but gave her up (much to her dismay) because they were from separate Clans and he couldn't be a great warrior if he was seeing a cat from another Clan. They grew to hate each other, and now Heathertail and Breezepelt may or may not be Just Friends.
In Omen of the Stars, Dovewing ends up liking both Tigerheart and Bumblestripe, who like her back. At the end of the main series, she has broken up with Tigerheart and chosen Bumblestripe as her mate. However, in Bramblestar's Storm, the Super Edition that takes place after the series, Bramblestar notices that Bumblestripe and Dovewing seem to have had an argument or something, and that Tigerheart and Dovewing spent a lot of time talking at the Gathering...
Water for Elephants: Jacob feels guilty about his attraction to Marlena at first because he is loyal to August, but when he realizes how dangerous August is and how he mistreats Marlena, he grows to hate him. However, he has to pretend to still be loyal to him to protect the two of them, as well as his other friends in the circus. Marlena struggles with her residual feelings for August before finally realizing that he's terrible and Jacob is far better, but must also keep up pretenses so they don't all get fired and/or killed. Phew.
All of Elayne, Min, Aviendha, and Rand's angsting before they settled on a polyamorous relationship.
There was also Berelain's determined pursuit of Perrin, which utterly trashed his relationship with Faile, and the whole complicated set of customs and rules that put Bain, Chiad, and Gaul in their position.
Egwene leaves the White Tower and realizes her feelings are for Gawyn and not his brother Galad. Both brothers are loyal to each other and both have feelings for Egwene, but she only reciprocates Gawyn's feelings.
Wicked: Mentioned a few times in later parts of the the book as the eventual state of the relationship between Elphaba's parents (Frex and Melena) and Turtle Heart. Elphaba suspects that her parents' uncertainty over which man was little sister Nessarose's father is a large part of why Frex favors the younger daughter after Turtle Heart's death.
Elphaba: You were in love with him. Frex: We both were, we shared him. Your mother and I did. It was a lifetime ago and I don’t know why anymore; I don’t think I knew why then.
In Wings of Fire, Starflight falls in love with two other dragons: Sunny, and later Fatespeaker. Sunny gently turns him down when he confesses because she sees him like a brother, and nudges him towards Fatespeaker, who reciprocates his feelings, and whom he eventually ends up with.
The Witcher has a long-running and complicated one between Geralt, Triss, and Yennefer, Played for Drama. Geralt and Yennefer have been in love since The Last Wish, but in practice have an on-again, off-again relationship (in part due to Geralt tying their destinies together with the eponymous last wish from a djinn to save both their lives, so they're not entirely sure how much of their relationship is genuine). Triss seduced Geralt when he and Yennefer were "off", and Triss has carried a massive torch for him ever since. Thing is, she's also Yennefer's best friend and she frequently hates herself for loving Geralt.
In the Xanth novels, Dolph, Nada, and Electra have this relationship. One of the books spells out the problem (with the solution not in sight, even though it is eventually resolved): "Electra loved Dolph, and Dolph loved Nada. Nada didn't love Dolph, and Dolph didn't love Electra."
