One easy way to cause problems for a friend group is to introduce a Love Interest. Said Love Interest will catch the attention of two or more members of that friend group. Soon friends will become romantic rivals. This trope allows writers to create drama in a story and add a level of depth to a Love Triangle or Love Dodecahedron.
This rivalry can be resolved in a number of ways. The love interest may pick one of the friends. The other could step aside, feeling it's for the best. It's also possible for the love interest to end up with neither. Perhaps they aren't interested in the other two. Sometimes, they may put their friends first, before a love interest. Another possibility is that the love interest gets together with both, resulting in Polyamory. In that situation, expect to see some Threesome Subtext and One True Threesome. The fact that friends are in love with the same person could indicate that they have similar personalities.
Compare Friend Versus Lover, Friendship-Straining Competition, and Lover Tug of War. A sister trope to Sibling Triangle. Can be the cause of We Used to Be Friends and a Cock Fight. Depending on how serious the competition gets, expect to see Removing the Rival. Can result in a Feud Episode if it lasts only one episode.
- In Bokurano, Moji and Nagi are both in love with their mutual friend Tsubasa, with whom they'd had a platonic friendship until they'd reached the age in which they became interested in girls. In the end, after Moji dies piloting Zearth, his heart is transplanted into Nagi.
- GTO: The Early Years: In the "Shonan Love Story" arc, all the boys (except Tsukai and Kamata, her brother) are trying to impress Kaoru and fight off the other guys interested in her. When she goes to the bathroom, everyone gangs up on Makoto, and then beats up Kamata for trying to prevent them from going out with Kaoru. The remaining guys (Ryuji, Eikichi, and Saejima) leave with Kaoru, and continue fighting for the right to go out with her. Keep in mind, these guys are Vitriolic Best Buds to begin with.
- The fallout of Sakura and Ino's friendship in the backstory of Naruto is the result of both of them crushing on Sasuke. After their fight in the Chunin Exams (which ends in a draw), the two repair their friendship and have far more of a Friendly Rivalry. At the end of the series, Sakura ends up with Sasuke, while Ino gets with his Suspiciously Similar Substitute, Sai.
- Subverted in Negima! Magister Negi Magi. Yue ends up falling in love with Negi while trying to Nodoka get together with him, but the two girls refuse to let it affect their friendship and spend more time trying to help each other than they do pursuing him themselves. Nodoka even comes up with a rather... interesting solution to try and bypass the rivalry which sequel series UQ Holder! shows that Yue was totally on board with and at least one timeline has the three of them in a polyamorous relationship.
- In Puella Magi Madoka Magica, Hitomi starts off as an out-of-focus good friend of Sayaka and Madoka. However, after she realises that Sayaka has feelings for Kyousuke, she quietly sits her down to sadly tell her that she likes Kyousuke, too. Neither can stop shake their feelings for him and though Sayaka eventually feels forced to step back and let them be happy together, her jealousy and depression also keep her from ever being friends with Hitomi again.
- Sinbad: Legend of the Seven Seas: Proteus and Sinbad were boyhood buddies growing up in Syracuse, Greece. But Proteus is a prince, the heir apparent to the throne of Syracuse, and betrothed to the lovely Miranda. Since Sinbad cannot hang out at court nor woo fair Miranda, he goes to sea, to become a renowned adventurer and buccaneer. However, Sinbad is willing to risk life and limb to recover the MacGuffin from the wicked goddess Eris, and Miranda accompanies Sinbad (initially as a stowaway). Proteus gets the MacGuffin back, and Miranda sails off with Sinbad and his slobbery dog.
- Catch That Kid: Gus, Austin, and Maddy are all friends and both Gus and Austin have feelings for Maddy. She plays on this, giving them each half a locket and telling them that she has the other half, in order to get them to help her with the robbery. In the end, they find out and ask her who the better boyfriend is: she runs away before choosing.
- Easy A: Rhiannon turns on her friend Olive after she catches her on a date with a boy she liked. Rhiannon joins a group of fundamentalist Christians who protest Olive for being promiscuous, despite earlier proudly proclaiming herself a super-slut.
- This Means War!: The film revolves around two fellow CIA agents and friends, Tuck and FDR, both falling for Lauren. The two compete for Lauren's affections, even using CIA technology in order to best the other. In the end, she chooses FDR. However, Tuck gets back together with his ex.
- The Layover: The premise of the film is that two friends, Meg and Kate, compete for the affections of Ryan. Ryan ends up sleeping with both of them. However, he treats this as a one-night stand and it's revealed he was engaged throughout the whole film.
- Love, Actually: In the Juliet, Mark, and Peter story, Peter marries his longtime girlfriend Juliet, who they both believe Peter's best friend Mark hates. In reality, Mark is in love with her and will likely always be, even if he's decided to give up on her. He reveals all of this to her on Christmas Eve silently, using cue cards, as he visits her and Peter's home. When he leaves, Juliet runs after him to give him a quick kiss in brief acceptance of his feelings, before going back inside.
- Most of the Heroic Bloodshed gangster drama, Shanghai Grand, revolves around the two main heroes, Man-Keung and Ding-lik, both of them being small-time hooligans who made it big in the Shanghai underworld and killing their way to the top. But unfortunately both of them fall for Fung Qing-qing, the daughter of their boss, and the subsequent Love Triangle ends up going horribly wrong for both men.
- In both the biopic Michael Collins and in real life, leading IRA figure Collins and his good friend Harry Boland both try to romance the same woman. She prefers Collins, and both this rivalry and politics slowly drive a wedge between the two men.
- House of Anubis: At the beginning of season 1, Amber was dating Mick and her best friend, Mara, had a crush on him. The drama gets started pretty quickly, as she gets jealous when Mick wants Mara's help as a study partner and later gets her the same bracelet she got him. Despite briefly making up, the rivalry started again as soon as Amber got confirmation that Mara liked him. They spent most of the season fighting and competing for Mick until Amber finally decided that she and Mick weren't compatible anyway and made the effort to patch things back up.
- How I Met Your Mother: Early on, Ted dates Robin until they break up in Season 2, and then in Season 3, Barney accidentally sleeps with Robin which got Ted mad because he broke The Bro Code rule of not to sleep with your bro's ex-girlfriend. Fortunately, the two kindle their friendship and Ted gives Barney his blessing to date Robin after he noticed that Barney does have feelings for her. However, Barney and Robin break up in Season 5 only for their feelings with each other rekindled in Season 8 where Barney proposes to Robin to marry him. At that point, Ted's feelings for Robin return and he's stumped when he received news of Barney's and Robin's engagement. In the last season, Barney confronts Ted about whether he still has feelings for Robin after he saw him holding Robin's hand in the previous season. Ted admits he still has them but he reassures him that he's helping Robin as a friend and promises he won't do anything to get between them and that he will try to let those feelings go which he did before the wedding day.
- Saved by the Bell: In "The Fight", Zack and Slater end up quarreling due to their shared interest over a new student, Joanna. After much humiliation from both sudes, the two eventually have a fistfight. Ultimately, she refuses both of them due to their fight ruining her time at a new school.
- Victorious: In one episode, one of Beck's friends from Canada comes to visit. Tori, Cat, and Jade, who are normally friends (though Tori and Jade are more a case of friendly enemies) all start competing with each other. Eventually Beck calls them out on their behavior. Tori and Cat apologize, though the episode ends with Beck's friend hooking up with Jade.
- In A Midsummer Night's Dream, Hermia wrongly thinks this is occurring in the wood when her beloved Lysander inexplicably jilts her in favor of her best friend Helena. She assumes Helena must have seduced him, not knowing that actually he's been enchanted by Puck and that Helena wants nothing to do with him.
- The Winter's Tale is another Shakespeare play where one character wrongly assumes this is happening, as King Leontes thinks his queen Hermione is cheating on him with his best friend King Polixenes.
- In Wicked, Elphaba and Glinda's close friendship is strained but not broken by Elphaba's choice to rebel against the Wizard while Glinda allies herself with him. What finally turns them against each other is that Glinda's fiancé Fiyero, whom Elphaba has secretly loved for years, leaves Glinda for Elphaba, and Glinda retaliates by helping the Wizard set a trap for the "wicked witch." They reconcile in the end, however, after Fiyero is seemingly killed by the Wizard's forces.
- In Girl Genius, Gilgamesh Wulfenbach, heir to the Pax Transylvania and Prince Tarvek Sturmvoraus, heir to the Lightning Throne, are former childhood friends who both vie for the titular character Agatha Heterodyne's favor. All three in this love triangle are young, talented, and meteorically rising top-class Sparks. Though the two men have longstanding grievances towards each other due to political differences, leftover issues from their childhood friendship, and general personality differences (Gil is blunt and forceful like his father, Tarvek is a conniving snake like his whole family), they both can agree to put them aside to take up Agatha's cause against The Other, all while still trying to subtly one-up against each other in Agatha's regard.
- Danny Gonzalez: Subverted in "I'm in Love with a Creeper". When Danny and his friend Kurtis Conner both arrive in Minecraft, they simultaneously fall in love... with a Creeper. Half of the song is spent with them in separate areas singing about their new love. When they both discover that they're in love with the same "chick", Danny briefly asks if they need to fight... and the idea is quickly ditched in favor of having a threesome.
- Parodied in The Fairly OddParents episode "Love Triangle", in which Poof and Foop are just beginning to move past their animosity and become friends over a mutual dislike of theater when new student Goldie Goldenglow arrives. The two of them are instantly smitten, and Foop declares, "Friendship over, I saw her first!" and they begin fighting for her attention.
- Family Guy: In one episode, Quagmire accidentally pocket-dials Peter as he confesses he loves Peter's wife Lois. At first, Peter tries to forget what happened, but can't let go of it. Eventually his anger towards Quagmire escalates to the point that Peter beats him up.
- Many Popeye cartoons begin with Popeye and Bluto on friendly terms, until they meet Olive Oyl and start fighting for her affection.
- The Random! Cartoons short "Hero Heights" is about two boys in a neighborhood of superheroes named Smart Alec and Strikeout turning against each other when they both fall in love with a new neighbor named Olympia. They end up returning to being friends after Olympia finds out that they had been picking on the other girls in the neighborhood and punishes them for it.
- Played with in Total Drama. Courtney was already paranoid in Action that Gwen has a crush on Duncan and they aren't particularly good friends back then. In World Tour, they set aside their difference and become friends for real... until Duncan comes back in the competition and cheats on Courtney with Gwen, prompting Courtney to swear vengeance and focus narrowly on getting Gwen out of the game. They only become friends again two seasons later, but there their friendship is ruined again for entirely different reasons.