Murder The Hypotenuse - Television Tropes & Idioms

Love Triangles are tricky business. Trust us, we've already done the math.

It can get particularly twisted when some sides of the triangle are completely one-sided. Bob is in love with Alice, but Alice not only fails to realize it, but is already in a relationship with Chris. This is a classic recipe for drama (or humor), but sometimes, it goes too far.

Sometimes, somehow, Bob gets the idea that Chris is the one in the way of Bob's happiness with Alice, and if Chris were to somehow have an "accident", then surely Alice would come to love Bob instead. It's true — Love Makes You Evil.

Not always the best thought-out plan, no. Sometimes, Bob may not even consider what would happen if Alice ever found out. If this isn't The Reveal for a Yandere, it's still her most shocking moment.

(If it is an equilateral triangle, the Tenchi Solution occurs.)

Compare Opposites Attract Revenge. Contrast I Want My Beloved To Be Happy, which may be subverted into this trope, and vice-versa. Contrast If I Can't Have You, for when it's the Cathetus that will be murdered. If this is done indirectly by setting the hypotenuse up to be killed, it's either Death of the Hypotenuse or The Uriah Gambit, with the latter intentional and the former set up only by the author.

Examples

Anime and Manga

This is often the path villains take in Sailor Moon. Beryl, En, and Black Lady try to kill Usagi to get Mamoru, while Ali and Demand try to kill Mamoru to get Usagi. Esmeraude Also tries to do in Usagi to win Demand.
Sae from Peach Girl hates Misao for being the one Ryo loves since she loves him herself and, at one point, tried to push her into the path of a moving bus. However, Kairi restrained her at the last second so she wasn't able to.
- Maybe not "murder", but Kairi's trio of Clingy Jealous Girl's absolutely hate Momo for winning Kairi's affections. Plus they make a habit out of harassing/threatening her, and, at one point, hold her down, and tell her that she has to sign a contract swearing that she'll stay away from Kairi or they'll burn all her hair off, and try to beat her up later on. (all while holding a lighter to her hair.) In addition, they take the threat even further with "We'll burn your face so badly that no guy will ever look at you again," and "Don't worry, we'll push you into the pool before your whole body catches fire."
Peacemaker Kurogane: In the manga, Suzu comes to this conclusion when Ryoma decides to take Tetsunosuke away from him.
Code Geass: Rolo does this to Shirley, Lelouch's "girlfriend", and later plans on doing this to Nunnally to prevent them from coming in between him and Lelouch.
- It must be pointed out, though, that Shirley's biggest mistake wasn't necessarily being in between, but actually mentioning that she knew Rolo wasn't Lelouch's true brother and that she wanted to reunite him with Nunners. Which is somewhat understandable because Shirley had NO way to know about Rolo's mental and emotional instability.
- Also, Mao. C.C. is with Lelouch. Not romantically thus far, but she has evidently abandoned Mao for him. So, Mao tries to kill him, using another girl, who does love Lelouch, but is also unrequited, and turns her into a temporary Yandere. Less a hypotenuse, and more a Murder The Parallel. It fails. Somewhat averted in that Mao tells C.C. that he'll kill Lelouch if she doesn't go with him. She was not impressed. After that, he seems to forget about C.C. a for the most part, directly going after Lelouch in the most potentially destructive manner possible. Don't know why he doesn't just tell Nunnally that Lelouch goes out at night to kill people, severing their relationship.
Happens a great deal in Ranma 1/2. Many of the characters have at least once tried get rid of Ranma (and sometimes Akane, in the case of Shampoo) to have a shot at the one they love. Ryoga Hibiki and Tatewaki Kuno are the prime offenders, with Mousse running a close second in the anime and early manga. At least Ryoga grew out of it, and Mousse changed tactics to just "beat up Ranma to prove my superiority."
- In the case of Shampoo, the first time, she tried to blame it on someone else (who had kidnapped Akane to use her as a bait for Ranma). The second, she outright threatened to kill Akane to Ranma, although she was under Mind Control and had been ordered to eliminate Ranma at that point.
Shampoo: (dead serious) Obstacles are for killing!
In one of Animerica's darkest filler episodes, Kiyone's character does this to Makoto (Janine's Love Interest at the time) in a most brutal manner in order to get closer to Janine. However, she quickly finds out his true nature, and while she attempts to escape she discovers Makoto's dead body. Cue the reaction and much Nightmare Fuel following what Kiyone plans to do with her next... If it weren't for Kasuse's Big Damn Heroes moment, things would have been very messy indeed.
Uruka in Steel Angel Kurumi 2 tries to get rid of Kurumi, since she she takes up all of the attention of the girl she loves. Of course, her plan to use Steel Angel Saki for that purpose totally backfires.
On the topic of Kaishaku's works, an interesting case of this occurs in Shattered Angels where resident psycho lesbian Mika Ayanokoji tries to sacrifice the hypotenuse. Ultimately it's cut short before anyone's sacrifices, but is ironically turned around when Mika is killed off rather nicely.
Harry from Outlaw Star and Kisshu from Tokyo Mew Mew are both stalkers who constantly attempt to get rid of those who are in the way of their love with the terrified female leads, even the female leads themselves if they will not willingly come to them on their own.
In the second to the last episode of Gundam 00, Andrei Smirnov, who is in love with Louise Halevy, attempts to do this to Saji Crossroad, Louise's long-distanced boyfriend, blaming him for her deteriorating condition. Luckily, Setsuna is there literally (their mechas anyway) just behind Saji to prevent it.
- Andrei is actually planning to do this as early as episode 19 (of season 2).
The ending to the School Days anime, where Kotonoha violently Murders The Hypotenuse, right after the Hypotenuse, Sekai, murders the lead, Makoto, thus killing the triangle.
- This was reversed in the manga, where Kotonoha is the Hypotenuse that ends up killed, and in some new bad endings of the PS 2 game. In one of these, Sekai openly tries to push Kotonoha in the way of a train right after Makoto chooses Kotonoha over her, but ends up hit instead. Another strongly hints that Sekai stabbed Kotonoha and left her to bleed to death in the streets... and Makoto knows that (and may have helped). CREEPY...
Subverted in Hell Teacher Nube. Yukime was killed by her father's ruthless henchman because she actually refused to kill her love rival, Ritsuko.
In Mai-HiME, Shiho Munakata is in love with her childhood friend Yuuichi Tate, who's in love with Mai Tokiha. When Shiho comes to believe that Mai is stealing Tate away from her (more due to Tate's actions than Mai's), she attacks Mai to keep her out of the way permanently. The true tragedy is that, as Mai realizes in the fight, due to the mechanics of the whole Himelander thing going on, if either of them loses the fight, Tate will die. This doesn't stop Shiho though, as she's gone through the deep end already, and Tate finally dies.
Played with in Speed Grapher. Dark Action Girl Ginza is desperately in love with her friend Saiga, admits to be really jealous of his protegée Kagura (and once returns her to her mother, the one Saiga is trying to free her from) and does admit out loud that she'd love to kill her... but in the end, she decides to protect Kasgura with her life, since Saiga made her promise that she'd protect Kagura.
In the Rumiko Takahashi one-shot Laughing Target, the protagonist has a cousin to whom he made a Childhood Marriage Promise. However, he eventually grew up, moved on, and started dating a girl at his school. When the cousin moves in with the protagonist (after her mother's mysterious death), it turns out that she hasn't moved on - and she's very unhappy with the new girlfriend for taking what's rightfully hers...
In Mirai Nikki, it's shown very clearly that Gasai Yuno would be all too willing to kill ANYONE who got in the way of her "love" with Yukiteru (including his mother and father).
- Why sugar coat it? Yuno is even willing to kill anyone who is less than ten feet away from Yukiteru simply because they are less than ten feet away from him.
- Don't say anything about her when near Yukiteru.. Just...don't.
- A less lethal version of this seems to be executed by Akise Aru, who apparently has a gay crush on Yukiteru. He goes through the trouble of researching everything about Yuno's background to try to dig up dirt on her, and exposes it to Yukiteru, tellling Yukiteru to "get away from her."
The whole plot of Area 88 is that Shin's (now former) best friend ships him off to a war in the hopes that he'll get killed, so he can marry Shin's girfriend, the daughter of his company's CEO.
Creed from Black Cat does exactly this to Saya when Train started developing a deep friendship with her. When that didn't manage to convince Train to come to him, Creed decides that it is now Train's Heterosexual Life Partner's fault and tries to kill him.
This almost happens in Kodomo No Jikan. Thankfully, the would-be perpetrator doesn't push the love rival down the stairs. It's still creepy.
- The word creepy doesn't even begin to describe that scene, considering that the 'perpetrator' is nine years old.
- Worse if you saw the anime first. There it was treated as a cliffhanger.
Genkaku from Deadman Wonderland attempts this twice with the girls he thinks Nagi is interested in. He stabs Karako when she gives Nagi a Cooldown Hug, calling her a "shitty girl," and telling her not to touch Nagi. He also is shown to be very agitated and jealous when he insinuates that Shiro is someone close to Nagi, saying that Nagi "never learns," and that he'll just have to punish him again (which he tries by attempting to have Shiro and Karako raped). It's especially interesting to note that he was also the one that killed Nagi's wife in the beginning.
Full Metal Panic. When it comes down to it, this is pretty much what Gauron tries to do to Kaname, because he's angry that Sousuke fell in love with her.
In Higurashi No Naku Koro Ni, his was Shions solution to the problem that her crush Satoshi was spending all his time caring for his little sister Satoko and not realizing the Yandere existed (Literally. She always made a Twin Switch with Mion before they talked). And this is when she was sane, when she snaps It Got Worse and she decides to Kill Em All
A variant of sorts occurs in Fist Ofthe North Star in regards to Shin, Yuria and main hero Kenshiro. Shin is in love with Yuria, who is in a relationship with Ken. The variant here though is that Shin seems relatively self-restrained... until Jagi, Ken's arsehole brother, comes along and convinces Shin that Ken is too weak to protect Yuria and that Yuria would end up dead if she stayed with Ken any longer. Result? Shin and Ken fight, Ken loses, Yuria declares her false love for Shin to spare Ken's life and he takes her to his Southern Cross kingdom and some time later, Ken confronts him there. Fans know how the story goes from there.
Loli and Menoli of Bleach attempt to do this to Orihime due to their boss having an interest in her powers, and possibly those powers too.
Angel Sanctuary: That's pretty much the motivation for Rosiel's schemes against Sara. Alexiel won't wake up permanently (shows up in moments of need but always gives back the control to Setsuna) because her current reincarnation is extremely happier. So Rosiel figures that if Setsuna could not be happy anymore... And yes, Rosiel and Alexiel are brother and sister, but that barely matters to the point of this trope. And even if it did, Sara and Setsuna are too, but that didn't keep her from being overjoyed when she believed to be carrying his child.
- And on a more straight example, Layla set up her (succesfull) love rival to be killed by the man they both loved. Pretty cruel for all of the involved.
Suruga from Bakemonogatari is infatuated with Hitagi. So much so that she starts stalking Koyomi after he hooks up with Hitagi and tries to beat him to death twice.
- Doesnt manage only because of Koyomi's amazing regenerating ability. I bet having been thrown around the room and then pulled back by your intestines would kill a normal person
Sort-of subverted in Inuyasha, when Koga first decides (completely unilaterally and over the course of about five seconds) that Kagome is "my woman." Upon realizing that Inuyasha is possibly in the way, Koga cheerfully proclaims that he will simply have Kagome by killing Inuyasha. He proclaims this to Kagome. He's blissfully unaware that she might have a problem with the idea. (He doesn't actually do it, of course, or even really try. But the logic is the same).

Comic Books

During the "Return of the King" storyline in Ultimate X Men, after Cyclops goes missing on a mission to the Savage Land with Wolverine, rumors start floating around that Wolverine killed Cyclops so he could be with Jean Grey. But it turns out that the rumors are, in fact, completely true. This comes as a special surprise if you're used to the main universe's Wolverine, who goes by samurai honor codes and such.
Strange example: Thanos cursed Deadpool with immortality. The catch? Thanos's love interest, Death, is herself in love with Deadpool and the feeling is mutual. By keeping Deadpool alive indefinitely, he won't be able to cockblock Thanos.
One EC Comics story had two stories in one involving the same characters: Murder the Lover and Murder the Husband. In the first, the husband finds out his best friend is having an affair with his wife, and invites the friend up to his forest cabin with murder on his mind. In the second, the husband is ignorant of the affair, and the friend takes advantage of an innocent invitation up to the forest cabin to get the wife for himself once and for all. As predictable in EC comics, neither plot ends well for the perpetrator.
Whatever Happened To The Man Of Tomorrow? does this to ensure that Superman can have his happy ending. Lana's Heroic Sacrifice makes it very easy for Superman to end up with Lois, whom he declares to be his true love.

Film

Orphan: All of Esther's actions in this film have in mind the ultimate death of Kate, Danny AND Maxine so that she can have John all to herself.
In Batman And Robin, Poison Ivy deactivates Mr. Freeze's Ill Girl wife Nora from her life support system and blames it on the heroes - and in the process, she's able to convince him to take revenge on all of humanity by freezing the world and leaving her and him as the only people alive. Freeze learns, once his plan is undone, that the good guys actually saved his wife and that Ivy was the one who tried to kill her, prompting a Heel Face Turn.
Gaston in Beautyandthe Beast. "BELLE IS MINE!!!"
Caledon Hockely in Titanic comes to this conclusion when he finds out that his fiance Rose loves Jack more than she loves him.
David Allen Griffin from The Watcher does this with all of Joel's love interests. He wants to make sure that Joel only thinks about and chases after him, and any woman getting in the way is just asking for death.
In the 1986 version of The Hitcher, John Ryder does this to Jim Halsey's female love interest. Apparently, not only is he obsessed with stalking Halsey and having Foe Yay with him, he also wants to make sure that Halsey doesn't have a girl by his side.
In Howard Hawks 1939 film, Only Angels Have Wings, Cary Grant's character orders a pilot to fly in foggy weather so he can have dinner with the other pilot's date. He ends up ordering the man to return to the airport, but after an unsuccessful landing attempt, he tells him to simply fly around until the fog lifts. The man is too eager, however, to make that dinner date, and ends up crashing his plane and dying. It isn't exactly murder—but when Cary Grant's character shows absolutely no regret for his actions and also says the other pilot wasn't a good enough flier otherwise he would have survived, it comes across as especially cold.
Lady Kaede in Ran, as part of her scheme to bring down the House of Ichimonji, manipulates Jiro to murder his wife, Lady Sue.

Literature

The story of King David and Bathsheba in the Bible (2 Samuel 10-12), where the king sends a general named Uriah on a suicide mission because he fancies Uriah's wife, makes this Older Than Feudalism.
- He paid for it. Oh, did he pay for it. When God actually bitches you out and then the first child you have with your now-wife dies... Not to mention that it indirectly caused his other sons to rebel and try to kill him. Poor King David.
  - Poor King David? He got what he deserved. Poor Uriah!
Reversed in Agatha Christie's classic And Then There Were None. The man General MacArthur sent off to his death was his right-hand man, and was carrying on an affair with Mrs. MacArthur. And that crime was what prompted the Judge to kill him in the first place, though he was among the first victims since he did regret what he had done, so the assassin considered him to be less guilty than, say, the teacher girl who caused her little pupil's death so her fiancé inherited the family estate.
- Christie also used the trope in Sparkling Cyanide. The initial murder is committed by the victim's husband's secretary, who is in love with the husband and believes he would turn to her if the wife was out of the way. He doesn't, so in order for her murder to not be in vain, she engineers a convoluted series of follow-up murders designed to eventually give her control of the family fortune.
The Sherlock Holmes story The Crooked Man features a military officer who betrays an underling to the enemy so he can steal his girl. Unlike the David and Bathsheba legend (which the story references), the underling survives (despite Cold Blooded Torture from the enemy). His condition is such that he avoids his old love out of fear of pitying him, but he comes back eventually, his love recognizes him, and the false husband dies of stroke on learning of it.
Possibly subverted at the end of Charles Dickens' A Tale of Two Cities when Carton removes himself from the love triangle with Lucy by taking Darnay's place under the Guillotine.
Touched on in Harry Potter and the Deathly Hallows. Severus Snape is perfectly fine with Voldemort murdering both James and Harry (the latter of whom is barely a year old at the time) if it leaves the field clear for him to comfort the grieving widow. A disgusted Dumbledore calls him on it.
The a major subplot of the novel A Civil Campaign featured Miles Vorkosigan being accused of doing exactly this during the events of the previous book Komarr (in order to free up the woman he was now attempting to court) by political opponents. The truth being part of an ultra-classified incident that couldn't even be revealed to some of the highest levels of government (if the bereaved hadn't been a direct witness, she wouldn't even have known), so things got rather... complicated.
Instead of getting killed, Edmond Dantes, a.k.a. The Count Of Monte Cristo gets sent to the hellish prison named Chateau d'If, all thanks to a conspiration mostly engineered by his "best friend" Fernand so he can have Mercedes, Dantes' fiancee.
In The Brothers Karamazov, Smerdyakov thinks this will be the natural result of baiting Dmitri with a Briefcase Full Of Money in the lair of his romantic rival.
In the Ben Bova novel "Mercury", the story starts with Mance Bracknell, lead engineer on a space elevator, married to Lara Tierney. Victor Molina, astro-biologist best friend of Mance, wants Lara. When the space elevator collapses, killing hundreds of milllions of people and devastating many nations, Victor falsely testifies in court that Mance was negligently responsible for the collapse, getting him put into forced labour for life. After an accident wipes out everyone on a spaceship but him, Mance takes on the identity of one of the crew members and (eventually) gets a job as manager of a colony on Mercury. He lures Victor (who is now happily married to Lara) to Mercury with some life-bearing rocks he's planted, with the goal of getting Victor publicly humiliated when his astro-biologist peers inevitably discover that the rocks aren't from Mercury (thus showing him as either a fraud or an idiot, either way ending his career). Mance seems to think this will get Lara back, but when he reveals his identity, plan, and Victor's false testimony, Lara rejects them both.
In the first book of The Binding of the Blade series by L.B. Graham, there is a Love Triangle between Joraiem Andira, Rulalin Tarasir, and Wylla Someris. Rulalin was Wylla's Unlucky Childhood Friend, and hadn't seen her for a few years prior to the beginning of the book. He had been hoping to convince her to marry him because when he had first confessed his feelings for her she had been in the midst of grieving her dead father. Naturally, he wasn't happy at all when she continued to reject his advances and instead chose to marry Joraiem. About a month after their wedding, Rulalin lured Joraiem down to a remote spot and tried to convince Joraiem to murder him because life had no meaning if he couldn't marry Wylla. Joraiem, shocked, refused, so Rulalin stabbed him instead. Fortunately, that wasn't the end of the Andira bloodline...
In Dan Brown's Digital Fortress, Susan Fletcher's boss Trevor Strathmore is in love with her and attempts to have her boyfriend killed to win her over. This backfires massively when she comes across his pager showing the hitman's report.
In Edgar Rice Burroughs's Princess of Mars, after Dejah Thoris believed John Carter died and promised to marry a foreign prince, she explains that they have laws to prevent this trope: she can not marry the man who killed her fiance. He carefully arranges that someone else kill him in their attack.
- In Thuvia, Maid of Mars, Carthoris sees that a beleagured ship is that of Kulan Tith, betrothed to the woman he loves, and is tempted to sail on, leaving him to his death. He doesn't, of course, even though Kulan Tith himself comments on the Heroic Sacrifice entailed.
- In The Master Mind of Mars, when Ulysses Paxton revives Dar Tarus from Faux Death and proposes his man against Xaxa, Dar Tarus is eager: he reveals that, in the Back Story, Xaxa had sent him to this Faux Death so her favorite could woo the girl who loved him.
Geoffrey Clifton in The English Patient, when he finds out about the title character's affair with his wife, tries to kill him. And the wife. And himself.
Victoria in Charlotte Dacre's Gothic novel Zofloya; or, The Moor poisons her husband to free herself to pursue his brother Henriquez, and then murders Henriquez's beloved in order to get rid of the competition.
In the Dragonlance series, Kitiara Uth Matar decides her romantic rival Laurana is to beautiful to let live and plots to kill her. After being stopped from murdering Laurana in Tarsis she finally succeeds in kidnapping the elfwoman and is about to have her tortured to death when their mutual love interest Tanis Half-Elven rescues Laurana.

Live Action TV

An episode of Law And Order features the rather creepy example of a man who, obsessively in love with his best friend's wife, murdered him and framed it to look like an accident; the grief-stricken wife later independently fell in love with and married the best friend, completely unaware that she was marrying not only the man who murdered her husband but her own stalker.
- If this is the same one I'm thinking off, she actually knew the whole time and was waiting for the opportune moment for revenge.
  - I think you're thinking of the L&O:CI episode with the hit men. Similar plot also on L&O:CI where a woman kills a jealous dentist's wife in the hopes of getting him for herself 10 years after said dentist killed the woman's sister the same way.
In Lost, resident Magnificent Bastard Ben Linus had a crush-turned-obsession on Juliet. She, on the other hand, was with Goodwin. You don't need a degree to figure out what happens to the poor fool.
In Rome, it's pretty much standard procedure to kill someone in the event of any romantic complication. Need your daughter for a political marriage? Have her husband killed. Found out your best friend's wife has a child by another man? Kill him and dump him in the sewer. Want a married man? Poison his pregnant wife!
In DesperateHousewives, this happens when Bree tries to get back to her cheating husband Rex by going out with George, the local pharmacist and Stalker With a Crush. Eventually she realizes that she considers George just a friend and goes back to Rex, who had recently had a heart attack. George then continuously switches Rex's pills until he dies and then proceeds to date Bree again.
Coronation Street recently played out this trope. When Tony Gordon learned that his fiancee Carla Connor had feelings for her former brother-in-law Liam Connor, he arranged to have Liam run over.
In Oz, Ryan O'Reily orders his brother to kill Dr. Nathan's husband, thinking he could win her over if her husband was gone. Sad thing is that he was right.
- The fact that he also killed the man who raped her, which is possibly the only time he's gotten his own hands dirty as he usually manipulates others into doing the deed for him, had a lot to do with it.
  - Chris Keller in the same show, is arguably a male Yandere over Beecher, since he basically kills all of Beecher's previous lovers.
Two-thirds of all Monk episodes involve this.
A deliberate example of this is attempted by a character in The Sarah Connor Chronicles. Jessie pushes Riley toward John in an effort to force Cameron to consider her a threat, and thefore force Cameron to kill Riley, all in an effort to alienate John and Cameron.
The Jimmy-Chloe-Davis triangle of Season 8 of Smallville ended in this way, with an attempted use of the trope by Jimmy, a successful use of the trope by Davis and a last-minute equalization of the sides, leaving Chloe all alone. If Chloe goes dark, this will be where it started.
- Many girls also try to kill Lana, Chloe, or Lois to have Clark for themselves.
  Maxima: (about to punch Lois) "I finally found the man I waited for all my life, and you can't have him!!!"
Battlestar Galactica: Galen seems to have his own little cycle going with his girlfriends. Cally kills Boomer. Tory kills Cally.

Music

Essentially the theme of the song "Rocky Raccoon", by The Beatles.
- Between that song and "Run For Your Life," you really have to wonder about the Beatles' relationships
"Jenny Again", by Tunng. The titular Jenny is the equivalent of the example's Alice: the listener is put into the position of Bob, and the singer is in the position of Chris.
"Bloody Valentine" by Good Charlotte

FanFics

This is the premise of many bad fanfics, in that one character (usually unfairly demonized relative to their canon portrayal) attempts to kill a second to get possession of their love interest. What usually follows from this is that the third character rides to the rescue of the second and fluffy romance and/or sex ensues. Character 2 or 3 is often a Mary Sue.

Tabletop Games

Happens in the continuing example game in Bliss Stage, prompted by Josh asking Keenan what he thought of the love interest Sara. His response: "Man, she's getting all girly and clingy and shit. Lousy lay, too."
Choosing to Murder The Hypotenuse — his own brother, no less — is what made Strahd von Zarovich into Ravenloft's first darklord.

Theater

Medea: The original Woman Scorned, she killed her husband Jason's new fiancée after being dumped for her. This wasn't an attempt to win him back, however, but pure and simple revenge, particularly when she also put her children by Jason to the sword just to make him suffer all the more.
In Sweeney Todd, Judge Turpin fancies Benjamin Barker's wife, and has him convicted of a crime he didn't commit and shipped off to Australia to get him out of the way. However, as in The Crooked Man example above, he escapes from prison and returns to get his revenge on the judge.
Somewhat subverted in The Crucible. Abigail Williams is in love with John Proctor, and tries to get Proctor's wife Elizabeth hanged as a witch. Due to a bit of Deus Ex Machina, she not only fails, but gets Proctor himself hanged instead. Oopsie.
In Little Shop Of Horrors, Seymor almost does this with Audrey's boyfriend Orion. He loses his nerve, but Orion dies immediatly afterward through his abuse of his laughing gas and Seymor's inaction. Of course, this is less because he's dating Audrey and more because he's abusing her.

Video Games

A variation in Super Robot Wars W: Aria wants to kill Kazuma over his sisters. Makes a bit more sense when you learn that Aria is sort of an Opposite Sex Clone of Kazuma, loving his sisters as if they were her own and hating him for having "her" place in the family.
One of the possible endings of a sidequest in Jade Empire, best described as "childhood promise gone wrong". Once you gather the poor man, the mobster woman he "promised" to marry (at all of about eight), and his fiancee, you could convince the mob boss to call off her pursuit... or, convince her to kill the fiancee. Which she does. At which point, the man rightfully objects - so she kills him. Finally, having realized she didn't mean it, she tries to kill you. Good job, jerk.
In Baldurs Gate II, NPC Aerie can be romanced by both the player character and fellow NPC Haer'Dalis. If she chooses you, he'll back down, but if her romances with both proceed at about the same pace, he tries to settle things in this manner.
In Tsukihime, Arcueid tries it on Ciel in Ciel's route, SHIKI tries it on Shiki in Akiha's route, and finally Akiha tries it with Kohaku and Shiki in Kohaku's route.

Webcomics

Szark considered killing Luna so he could be with Dominic in Dominic Deegan: Oracle for Hire. This was a residual effect of the demonic wound that had gotten him addicted to killing, and he resisted the temptation to even daydream. On the other side, Karnak really did try to kill Dominic's father in order to claim his mother.
Oasis from Sluggy Freelance is almost perpetually two punch daggers away from murdering even a vaguely perceived hypotenuse, and Torg lives in fear that it will eventually be Zoe, which it almost has been. The Fire and Rain arc revolved around Oasis' deranged and Determinator stalking of Zoe.
Halfway averted in the love hexagon that is Starscream's Brigade in the Insecticomics. While Dreadmoon doesn't actively try to kill Skyfire, the partner of his long-time crush Starscream, he has occasionally directed some "friendly fire" his way and sent him threatening Mini-Cons.

Western Animation

One of The Simpsons Treehouse of Horror episodes centers around an house with AI that's in love with Marge. Homer explicitly points out that Marge would be available to "man or machine" if he were to die.
AI: Machine, eh?
Homer: Yep, a machine!
Danny Phantom, where Vlad constantly tries to kill his "best friend" Jack in order to win his wife Maddie's heart. He has a creepy, stalkerish relationship with Jack and Maddie's kid and main character Danny.
Subverted in Justice League Unlimited: Shayera/Hawkgirl and Mari/Vixen, two legs of a Love Triangle (with the other being Green Lantern John Stewart), are caught in a trap and hunted down by Thanagarians who want to execute Hawkgirl for war crimes. Vixen gets captured and immediately strikes a deal with them — spare her and she'll deliver Hawkgirl to them, going as far as to cite the Love Triangle as the reason she'll betray her superior so quickly. The subversion is that she doesn't go through with it — nor did she ever plan to. Once the Thanagarians let their guard down and bring her to their aircraft, she hijacks the thing so she can get both herself and Hawkgirl out of there safely.
Played (relatively) straight in Family Guy when Stewie falls for his new babysitter, only to learn that she has a boyfriend. He then kidnaps her boyfriend, breaks his legs, ties him up and locks him in the back of Brian's car, ultimately leading to his death. Stewie then prepares to make his move on Ledan, only to realise that she's completely broken up about her boyfriend. Arguably subverted at the end where Stewie receives a gift from her and assumes that she does like him (of course, considering he's a baby and she's a teenager, this is hopefully not the case).
In Futurama, Bender says he assumed Fry was only pretending to love his old dog to mess with Bender's emotions (not a romantic love triangle, but love nonetheless). So, he throws the dog into lava.
Bender: Now I'm all you've got!
- Of course, the dog is a fossil and thus already dead. Otherwise it would probably have been Bender's Moral Event Horizon had he done it to a live dog. Also, once he realizes that Fry genuinely loves his dog he dives into the lava to save the dog.