Trinity: You wanna make a deal? How about this? You give me Neo or we all die, right here, right now. Persephone: She'll do it. If she has to, she'll kill everyone here. She's in love. The Merovingian: It is remarkable how similar the pattern of love is to the pattern of insanity.
School Days... for the love of GOD, do these two girls go axe-crazy over this guy-to the point that they'd happily murder each other in broad daylight, with witnesses, just to be rid of the competition?!
Dr. Tōfū in Ranma ½ would begin acting bizarrely whenever Kasumi Tendō is around, or even simply mentioned. This makes him very dangerous as he'll often be in the middle of treating a patient, and once bent Ranma's neck at a ninety degree angle.
This also covers Ranma's fiancées (Akane, Shampoo, and Ukyō) fairly well. When first introduced to the series, they conduct their courtships in a relatively calm, normal fashion. As Ranma continues to ignore them, they slowly grow more desperate — and more extreme. Magic, deception, violence, all of these become legitimate avenues of pursuit towards romantic happiness. Ranma's rivals, meanwhile, enter the series in this state.
Kodachi Kunō, on the other hand, was already crazy before love even entered the picture.
Mazinger Z: Dr. Hell can be a subversion because he was already quite unstable and troubled before... but when he was in college and fell in love with a cute Japanese exchange student he started behaving obsessively (getting angry if someone dared to spend time with her) and erratically (his grades started slipping because he was too obsessed to study). And when he found out she was in love with another person, he flipped out completely and tried to Murder the Hypotenuse (and even stormed into the campus with a shotgun!).
Boss also tended to act in a very dumb, irrational and even obsessive way when he was in presence of Sayaka or Jun Hono. Sayaka tended to ignore it, but Jun did not appreciate it or find it amusing.
Brock in Pokémon, who is usually the rational Big Brother Mentor to Ash and Misty (or May, Max and Dawn), tended to lose his cool around beautiful women; especially Nurse Joy or Officer Jenny (and since both are everywhere, this quickly became a running joke with him proclaiming the latest one was the fairest of them all).
It's not that they are everywhere, it's that either their mother's had the worst pregnancy's ever, or there are large cloning facilities somewhere. Very early on (we are talking the first few episodes of season 1) one of the Officers Jenny shows Ash a graduation picture of somewhere around 30 women (all of whom look identical to Officer Jenny, all of whom are named Jenny) who are graduating from the Police Academy. If I remember correctly there was also one of these shown for Nurse Joy, but for nursing school.
Jenny and Joy are their family names, and are mostly either sisters or cousins.
Strawberry Panic!: Shizuma (aka Etoile-sama) can make Nagisa freeze or even faint just by looking at her a certain way. Typically the character who has this effect on a person is unaware, but Shizuma knows and seems to like doing this.
One Piece: Boa Hancock badly misinterprets innocuous actions as signs that Luffy reciprocates her love for him. This would seem cute and innocent and so not creepy if she didn't happen to be pushing thirty. Her behavior has a uncomfortable resemblance to a certain Real Life psychological disorder. (Then again, given all the crap she had been through early in life, her screws may not have been put in quite tight enough before she met him anyway...)
One of the creepiest examples comes from Minoru Murao's Knights. Of all people, Nina, the cute little girl of the cast goes nuts when she assumes that the object of her affection Mist is physically involved with his Ms. Fanservice companion Euphemia. Her response is to lead a supernatural agent of the Corrupt Church (the same Church that nearly burned her at the stake after accusing her of being a witch) to kill him. She even shoots him in the leg with a crossbow. Her motivation? To send his soul to Hell, where it will be "purified", then join him in death so they can be together for all eternity. Keep in mind that this guy saved her life in the first few chapters, which is why she's so hung up on him in the first place. This is borderline Love Makes You Evil. To her credit, she does eventually realize just how utterly screwed up she was, and works to undo her actions.
Fruits Basket: Kagura Sohma is the sweetest little thing... until something gets between her and Kyo....
In Basilisk, Action Girl Hotarubi is... well, not exactly "there" when something bad happens to her husband, Yashamaru. And she ends up dead because of it.
Not to overlook Kagerou, who gets insanely jealous of Oboro enough to even attempt killing Gennosuke. Oboro's choices may also be love-crazy, depending on your perspective.
Funny, because Oboro was Genre Savvy to actually recognize this trope and temporarily blind herself to NOT invoke it on her own clansmen.
Lucy's love for Khota in Elfen Lied drives her to go insane and murder his dad and little sister. She was partially insane before that anyway though. With her dog being murdered before her eyes, and all.
Well he was there to save her and not anyone else, so when he transformed...
Zetsuai 1989 is all about this trope. Let's see: when Izumi was five, his mother discovered his father was cheating on her, and murdered him in front of Izumi so that she could "possess him completely". Then there's the Yandere fan Eri, who tries to murder Kouji at his farewell concert. And that's without even mentioning the multiple examples of Kouji being driven to despair, self-mutilation, or generally self-destructive behaviour because of his love for Izumi — who is understandably a bit freaked out by all this. At first. After a while, he starts to join in...
Gunter from Kyo Kara Maoh. At first, Gunter seems a little like an idiot, or perhaps more like a teenage girl in love. He tends to be rather overprotective of Yuuri, fussing over every little thing and freaking out whenever he goes missing. Supposedly (at least in the manga), Gunter was actually quite the organized, professional man before he met Yuuri.
And in Wolfram's case, at least where Yuuri is involved, love makes you very veryveryprotective and clingy.
Saika actually has this as a power: she takes control of her main host by slowly wearing them down with incessant whispers and promises that she can give them any friend, companion or lover they want if they just sit back and let her handle it ("handle it," of course, being defined as "stab the target and infect them with The Virus so that they become an unquestioning slave to the Hive Mind"). It's only by virtue of being a Broken Bird that doesn't really get what love actually is that her current host, Anri Sonohara, has been able to resist it for five years and counting.
In .hack series, Harald's obsession toward Emma Wielant (even after his death) was what caused him to create the beta version of The World, Fragment, both of which are actually an attempt to create the ultimate AI by studying millions of players. And guess the source of the network crisis that happen throughout the series...
Mayo — 3rd Fushigi Yuugi OVA. She's so infatuated with Tamahome that she's willing to destroy his world (both literally and figuratively) just to be with him.
Poor Nina Einstein. She started as an inoffensive Shrinking Violet, only to develop a crush on Princess Euphemia after she saved Nina (and others) from terrorists, and went kinda loopy, earning her the label of The Scrappy among the fandom. Then things went worse: Euphemia is killed by the terrorist Zero, which sends Nina off the deep end, leading her to develop the world's first atomic bomb. It fails, but the Britannians hire her as a researcher, and eventually her perfected bomb leads to the destruction of a good chunk of Tokyo and the ten million people in it. Not helping matters at all is the fact that she was practically rabid in ordering its use up until she saw the Sphere of Destruction (and the 35 million deaths) it caused, only then getting her My God, What Have I Done? moment.
The ultimate cause of Tsubasa Reservoir Chronicle, as both motivation of the villain Fei Wong (who wants to resurrect the technically-not-dead Yuuko Ichihara and also at one point the motivation of the hero (it's crazy due to what they are both willing to do- it's evil, yes, but also completely fucking bonkers). At a specific point in the backstory the hero, in the madness of love, chose to turn back time so he could save the girl he was in love with. This act borked the entire time-space continuum.
Since the two series are connected ( as are their heroes), this means that love driving people nutso is also the source of Xxx HO Li C. It is, in fact, the source of the main character, since he is a duplicate of the Tsubasa hero created when time was fucked up.
Some fans theorize that even Cardcaptor Sakura was caused by this love driving people nuts, as it is suspected that it was all part of the plan Clow Reed set up to overcome Fei Wong's Evil Plan to resurrect the aforementioned not dead person. Needless to say, a plot driven by so many plan-happy nutjobs is not the easiest thing to follow.
Invertednote without actually being Love Redeems in the Wild Series. When they have a master, manbeasts will not lose their minds and attack humans, and that bond is based around love (whether they want itor not). So basically, love makes you sane in this case.
In ...Virgin Love, Kaoru believes this based on his mother's behaviour and shuns all emotional relationships for that reason. When it finally happens to him too, his lover is willing to accept the Crazy Jealous Guy side of him and persuades him to stay together.
However, the real winner is Jack Vessalius, whose obsession started the entire plot.
Puella Magi Madoka Magica has Sayaka Miki, whose love for a childhood friend is unfulfilled, driving her berserk, and eventually turning her into a huge mermaid monster. Though in her case, her love was just a catalyst; the poor girl already had SERIOUS issues from long before she was unfulfilled.
In the Rebellion movie, Homura's love for Madoka turns her into the devil.
Belarus from Axis Powers Hetalia is described as being relatively cool-headed. That, is, before she fell in love. She cornered Russia in a closet, made him cry, and carries knives in her dress to threaten people who get too close to him. Not to mention, he's her brother.
Shion in No. 6for Nezumi. When Nezumi is threatened, Shion switches from either all-out rage or coldly, completely rational and murderous. In the novels, he comes close to strangling a man when he tries to kill Nezumi and declares it to be "punishment." In episode 10 he murders a guy in cold blood who tried to kill Nezumi.
Ciel is implied to be this way for his fiance Elizabeth in Black Butler. Under any other circumstances, Ciel would not go anywhere near the big, creepy castle without Sebastian. Unless, of course, Elizabeth has gone missing and he has every belief that she is in there and in trouble. Then he'll do anything. Including giving Grell pretty much permission to rape Sebastian in exchange for backup. Not crazy enough for you? How about after he realizes all the girls in the castle are living dolls, he ditches Grell in order to run deeper? And still keeps looking for Elizabeth after being told he was next to be turned into a doll?
Still not enough proof? What about in the game, Black Butler: Phantomhive and Ghost Ciel nearly had a panic attack when Elizabeth fainted. He was so concerned about her that he fell asleep while looking after her unconscious form; a situation most likely not happen if it were another person.
In the manga, Ciel throws himself in front of a bear without a second thought to protect Elizabeth. This act also shows Elizabeth's mother, Frances Middleford, that Ciel is more worthy of being her daughter's future husband than she had originally given him credit for. Still, that could be considered more heroic than crazy, since Ciel knows that if he is in danger of getting hurt, Sebastian can easily save him.
Grell is like this for Madame Red and later Sebastian.
Koharu No Hibi: Koharu in regards to Akira. She stalks him, obsesses over him, and devotes her whole life to him. In chapter 21 she even told him she would die if he asked her to.
Ai no Kusabi has Guy, who is so in love with Riki, not only does he give Riki a penectomy to remove the pet ring that was on his penis upon being told that as long as Riki wears Iason's pet ring he'll never be free of him, but he also blows up an entire fortress in an attempt to kill Iason. Second example is Iason, who, like Guy, becomes extremely obsessed with Riki. It's not touched upon in the old OVA, but the novel and audio drama have scenes where Riki slept with a female pet, and he was subsequently brutally tortured by Iason. Not to mention the number of times Iason forces Riki into having sex with him.
One of the lyrics from the opening of Chuu 2 Byu says this.
In Naruto, this is revealed to be the true nature of the Uchiha Clan's curse, crossed over with Love Makes You Evil. They do not lack love; they love too much. And when they witness the death of a loved one, it activates the sharingan, literally born out of the hate that was born out of that loss. The deeper they delve into that hatred, the stronger their eyes get, but as a side effect they become hateful, bitter, cynical, and as Sasuke, Tobi, and to a lesser extent, Madara, has shown us, downright insane. This is why Tobirama Senju, the Second Hokage, considered them a "cursed clan".
K's Fushimi Saruhiko is the most insane character in the whole show ( aside from the Colorless King) and all just because he wants Yata Misaki to notice him. It goes so far that he does everything to make Misaki hate him just so he isn't ignored. When he is with SCEPTER 4 he's just a very snarky and rather cold young man but once Misaki pops up he goes into crazyobsessive"just notice me" mode.
In an issue of Swamp Thing, "My Blue Heaven" (written by Alan Moore) has Alec trapped on an alien world all alone. He uses his plant-controlling powers to create clones of himself... and then, in a moment of temptation, creates his love Abby. After spending another day creating an entire populated world, he accidentally creates a John Constantine who warns him how crazy he's become. It doesn't help that Alec can't ignore the fact he can't get Abby's smile just right, and he goes mad when his Abby-self responds "All love... is madness."
Parodied in Astérix and the Legionary, where Obelix starts acting extremely strange because he's in love with Panacea, which is soon diagnosed by the other villagers. Later, after their terrible behaviour has caused a centurion to become extremely overstressed and prone to collapsing sobbing onto other soldiers, he assumes he's in love. This seems at first to be Obelix's Cloud Cuckoo Lander personality, but it becomes a Running Gag with every other character who witnesses his freakouts assuming the same thing.
A more benign example: at one point in the My Little Pony: Friendship Is Magic fanfic Dawn of a New Day, Twilight Sparkle becomes so pent up over her inability to confess her feelings to Rainbow Dash that she enters a delusional state (complete with false memories) and spends several hours believing that she has and they are happily dating. Unlike other examples of this trope, she doesn't engage in any sort of violent or disturbing behavior and just acts more affectionate towards Rainbow Dash. Upon snapping out of it, Twilight is left feeling guilty and sad. Fortunately, her behavior helps Rainbow Dash to realize that she's starting to develop feelings for Twilight.
Megara: People always do crazy things when they're in love.
Film — Live Action
In the classic play and film The Dybbuk, Khonnen, a poor student, and Leye, a rich merchant's daughter, fall in love. But her father makes her marry a rich man's son. So Khonnen studies the Kabbala, and — using what is effectively black magic — dies and becomes a spirit who takes over Leye. (At the wedding, he makes her shout to the groom, "You are not my bridegroom!")
It's not romantic love, but Loki's love for his adopted father and home (and by extension, mother and brother) in Thor and his desire to be loved as a son on par with Thor drives all his schemes and ambitions (and the plot). He eventually becomes a (literal) Woobie, Destroyer of Worlds, and when Thor calls him out on his actions, his composure deserts him.
Thor: This is madness! Loki: Is it madness? Is it? IS IT??!!
In X-Men Origins: Wolverine, Victor did not take his brother James leaving him for a life of peace well... not in the least.
In Only the Ring Finger Knows, Yuichi Kazuki is known at Wataru Fujii's school for being kind and polite to everyone he meets, despite possessing ridiculous amounts of beauty, wealth, and talent. Yet whenever Wataru crosses paths with him, Yuichi never fails to be snarky and insulting towards him. Karin, Wataru's sister, comments that this must mean that Yuichi either really hates him... or really likes him. Guess which one it turns out to be.
Bellatrix Lestrange from Harry Potter could qualify for this, seeing as she's utterly obsessed with her master in an... "unhealthy way". Although she already had a husband, Word of God stated that Voldemort was her true love.
Richard and Jessamyn in Swordspoint, as well as Richard and Alec and basically everyone else in the book and its sequels to a lesser extent.
In Warrior Cats, there is Ashfur. After being dumped by Squirrelflight, he attempts to kill her father, and later her (adopted) children, to make her feel the same pain he did. When Jayfeather sees Ashfur in the feline equivalent of heaven, he protests that Ashfur attempted murder, and the response he's given is "Ashfur's only crime was to love too much."
Lydia in Caught In The Act by Peter Moore in regards to Ethan.
Vlad Tepes in Count and Countess. To get to Elizabeth Bathory's time period, he has to somehow outlive his natural lifespan. The measures he takes become increasingly more frantic and sadistic.
In The Dresden Files several characters suspect love was the underlying reason behind The Summer Lady's Aurora actions. Also the Winter Lady Maeve and the new Summer Lady Lily suspect that The Queen of Winter's Mab actions are motivated by love. And they are visibly disturbed by the notion. Maeve in particular implies that it is very dangerous for powerful magical beings of the Never Never to be in love. It twists their worldview and throws them completely out of their comfort zone.
It turns out that Maeve was lying and has been under the influence of Nemesis and that she and Aurora were infected with some as of yet unknown disease that makes those who are affected start to work for the Outsiders
In the Delirium Series, this trope is why love is said to be the reason for all of humanity's past ills. As a result, it is classified as a disease, amor deliria nervosa, and at 18 every person is required to get a surgery to cause them to be unable to love.
A central theme in The Twilight Saga. Both Edward and Bella fit this trope. To a lesser degree, Jacob as well.
Invoked by Katniss and Haymitch at the end of The Hunger Games. She needs the Capitol to think she pulled the stunt with the berries because she was crazy in love with Peeta, and not because she was trying to be rebellious and undermine the Games.
Played with in William Faulkner's A Rose for Emily. The townsfolk regard high-born Emily running around with a workman to have lost her head in love. Her later actions prove she was definitely cracked, but she might have been cracked well before falling in love.
Don't ever hurt or kill one of Willow Rosenberg's girlfriends, lest you want to end up flayed alive.
"Love makes you do the wacky." — said twice in the episode "Some Assembly Required". First time by Willow, in reference to Angel's jealous behaviour toward Xander, and then by Buffy, about why a classmate revived his brother as a sort of Frankenstein's monster.
In a later episode, it appears this is happening with Dawn when she falls for a jock. It turns out, there was a spell involved and Hilarity Ensues.
In Skins, Effy's love for Freddie literally makes her crazy: she's eventually sectioned for either schizophrenia, depression, or both.
Noah's Arc: Dre goes to crazy lengths to get Alex out of the picture so he can be with Trey, setting up a Batman Gambit to turn Trey and even Alex's friends against Alex. It's bizarre even by TV drama standards.
Often a case with patients in ER. After the death of his granddaughter caused by a crazy bomber who happened to be taken into the same hospital, the man who was previously shown to be friendly and calm went and strangled the guy to death. When Gates's best friend's wife finds out he was dating Neela, she got drunk, went to the ER and flew into a rage at both Gates and Neela. In another instance, when a man found out his girlfriend was dying, he brought in a gun and threatened the doctors working on her to continue working on her and bring her back, even though her heart had stopped.
Characters of As the World Turns often go to pretty extreme extents for their family and love interests. This is actually a standard trope of manySoap Operas, usually combined with Derailing Love Interests as heretofore normal, decent people, usually women, go completely off the deep end in an effort to hang onto or seek revenge on former love interests.
Bus Driver Stu Benedict, of The Adventures of Pete & Pete. Almost every time we see him, he's just been dumped by his on-and-off girlfriend Bus Driver Sally Knorp, and he reacts increasingly poorly. On various occasions, the break-up has caused him to spend the bus ride home giving a six-hour tour of important locations in his and Sally's life; go insane upon hearing "If Your Happy and You Know It"; and drive to the Arctic, tattoo her name to his chest, strap himself to an iceberg and drift out to sea (though we don't know if he went through with that last one. He shows up again afterwards, so he probably didn't.)
On Doctor Who, Rory loves Amy. A lot. Enough that he guards her sleeping body for 2,000 years without leaving.
Although that was arguably more like love keeping him sane.
River loves the Doctor. A lot. Enough that she almost destroys time in order to save him.
In Desperate Housewives, Edie, who up until that point was a casually promiscuous woman who was more bitchy and snarky than actually crazy. Once she starts having a liking for Carlos, suddenly she starts going completely insane and even attempts suicide just to get his attention.
In Flashpoint, the team regarded Valentine's Day as one of the toughest days with plenty of calls. Three cases are shown: a suicidal widower whose wife died on Valentine's, a mother taking her daughter's manager in a strip club hostage and a recently fired man who was madly infatuated with his boss.
The Haunting Hour: The Valentine's Day episode "Terrible Love" had Brendon go insane when Maggie begs Cupid to shoot Brendon with another love arrow. Cupid initially objects as one love arrow is enough, and more than one causes jealousy, greed, and possessiveness (which Cupid has seen too much of in his time as the god of love). Maggie doesn't care, and ends up dealing with her crush who has turned clingy and deranged.
Wizards of Waverly Place: Harper, before her much needed Character Development. This could also be said of Justin, ever since "Wizards vs. Vampires" - and is specifically stated as the reason why Justin didn't dump Rosie when he found out that Rosie was an Angel of Darkness.
Steven Curtis Chapman explains in "Something Crazy" that you don't know what love is until it makes you do something crazy. He mentions a street corner preacher, a humanitarian in Uganda, and the biggest one of all, Jesus Christ.
In the music video, he drags a piano around with him to her house. While it seems strange at first, observe how the piano could stand for the suffering for not being loved by her anymore. He reaches her house, to see her kissing another man. Depressed, he leaves, standing in front of a railroad crossing, playing the piano. Then, a train hits him, and he dies.
A more literal example of this trope, the song ''Talkin' To the Moon'' takes a similar approach to Grenade, but instead, it depicts a man who has been driven stark raving mad instead of being Driven to Suicide over a relationship. Here, the person is revealed to be talking to the moon...pretending the moon is his once significant other.
While the tone of this song is Lighter and Softer when compared to Grenade (though the music sounds sadder), imagine if you broke up with your significant other. You no longer have any interest in him/her. You've completely moved on and wish to find someone else. Meanwhile, that person you dumped is left emotionally compromised by your relationship with him/her, that he/she is driven mentally insane...to the point where he/she ends up talking to a figment of his/her imagination: You. He slowly deteriorates under his own delusions of being in love with you while you don't even know about it.
Polonius is initially convinced that Hamlet's recent wacky behavior is caused by his love for Ophelia. His attempt to set up a sting operation to prove his theory ends with an apparently-deranged Hamlet ranting that he'd never loved Ophelia, and that she'd best go be a nun (or a whore, depending on your interpretation). So much for that idea.
In A Midsummer Night's Dream, Helena is aware that her passion for Demetrius is wacked out even before she betrays Hermia and Lysander to him.
And as he errs, doting on Hermia's eyes, So I, admiring of his qualities: Things base and vile, folding no quantity, Love can transpose to form and dignity: Love looks not with the eyes, but with the mind; And therefore is wing'd Cupid painted blind: Nor hath Love's mind of any judgement taste; Wings and no eyes figure unheedy haste: And therefore is Love said to be a child, Because in choice he is so oft beguiled.
In Thrill Me, this trope is Nathan's explanation for why he committed a series of crimes, including murder.
But you've asked a simple question And I've told you why It wasn't on a dare or on a whim It's hard to comprehend now That the reason why Was simply that I went along with him
Salome, the former disciple of Makai Kingdom's Overlord Zetta, whose crush on said Overlord goes into this trope on the deep end. She willingly started channeling her own mana into Zetta without his knowledge or consent, slowly killing herself to make him stronger. Upon learning that Zetta has been cursed by The One and has only two days to live, Salome, who is dying herself, then tries to make Zetta marry her so they can die together...by crashing her own netherworld into Zetta's and eventually provoking him into killing her.
Persona 3's Yukari nearly dooms the world in an attempt to see the person she loved again.
In Prince of Persia (2008), the Prince destroys the trees that sealed Ahriman again to revive Elika. It's either a case of Love Makes You Dumb or Love Makes You Genre Savvy, as the epilogue Establishes that he did this because he knows the prison can't hold, and he'd rather face Ahriman now with Elika's help, then to face him without her down the line.
Craft of Mega Man Zero 4 is either this or Love Makes You Evil. He joined Dr. Weil's army only so that he can protect Neige, the girl he loves. When the latter fled from Neo Arcadia because of the iron-fisted rule of the Big Bad, he makes it his mission to bring her back (thinking that she will be safer in Neo Arcadia), all while spearheading Operation Ragnarok, which would obliterate any inhabitable area outside of Neo Arcadia. Neige did eventually talk Craft out of working under the Big Bad, only for him to destroy Neo Arcadia with the namesake of Operation Ragnarok, a Kill Sat, aiming for Dr. Weil. According to the Complete Works, that attack claimed thousands of lives.
This is how the original Blood Omen: Legacy of Kain begins: When Nupraptor the Mentalist, guardian of the Pillar of the Mind, discovers that his lover Ariel, guardian of the Pillar of Balance, has been murdered in cold blood, he goes completely insane and secludes himself in his mountain retreat. Which wouldn't be so bad by itself, except he has a mental link with all the other Pillar guardians, who all become corrupted by his madness in turn. Including Kain while he was still in the womb.
In Half-Minute Hero, the so-called "Beautiful Evil Lord" went completely insane after learning that his beloved Millennia was kidnapped by an Evil Sorcerer named Noire, and vowed to cast the spell of destruction because he felt that a world without Millennia wasn't worth living in. You, the Hero, come along and try to calm him down by beating up Noire and returning the Evil Lord's girlfriend to him. You can also attempt to try and tackle him head-on first to snap him out of it by force (and you get a Cosmetic Award title for doing so), but because the Evil Lord is hopped up on equal parts adrenaline and angst, you'll get beaten repeatedly unless you take enough time to Level Grind to the point where you can face him on equal footing.
And he goes insane again later when Millennia's transformation into a bat suddenly worsens.
Rule of Rose: Gregory loves his son Joshua. Therefore, after Joshua dies of unspecified illness, he becomes a crazed serial killer. Wendy loves Jennifer deeply. Therefore it's completely unacceptable for her that Jennifer could love anything even nearly as much as her, so she kills her beloved dog - for starters.
If Usso fights Laodecia in the final Space Scenario of Shin Super Robot Wars, Fala will show up, vowing to pay back the debt she owes Laodecia. When Usso protests, she tells the little boy to shut up, saying that only a strong man like Laodecia can satisfy her - and Tashiro wasn't up to the task.
This trope is the whole shebang of Silent Hill 2, where the protagonist James Sunderland is absolutely nuts following the death of his wife Mary... to the point where he's desperate enough to believe that she is actually alive and waiting in Silent Hill. Of course, his feelings toward Mary, inability to see her suffer, and all-consuming fears of abandonment are so exaggerated that he kills her instead of letting her die and is eventually Driven to Suicide, at least in one ending.
Tsukihime has Roa. Arcueid is so beautiful! How can I make her like me? Oh I know, I'll make her turn me into a Dead Apostle so I gain immortality, steal some of her power, turn her against every other being like her and then turn up in random towns for the next eight hundred years so she has to come find me and kill me! Man I'm smart, this is sure to work.
To be fair, at least in Ciel's route the implication is that he doesn't KNOW it is love.
Arcueid actually has the same trouble telling how she feels towards Shiki. She doesn't know why she gets all emotional around him, upset if he breaks a promise and spends so much time thinking about him. The idea is raised that maybe Arcueid hates him or something but that's obviously not the case.
Caster in Fate/stay night, who at one of her more sympathetic moments in UBW is extremely stressed over the actions she's been taking. They're horrible things she never would have done in life on top of her not believing her plan will actually work, but she's desperately struggling nonetheless. It would help if it was easier to read what Kuzuki was really thinking. It's not even entirely clear to the reader whether her affections are reciprocated.
EVERYONE! It's true that while Yasu A.K.A. Shannon, Beatrice, and Kanon may be the craziest since s/he planned the murders of everyone in the Ushiromiya family, as well as a few servants, and a doctor because Battler came to Rokkenjima at the wrong time, but EVERYONE has their moment where love drives them bonkers.
If you thought the School Days anime was bad for this, just try the original visual novel and one of its companion games, Cross Days. Now with multiple bad endings involving various kinds of sharp object. Or trains.
In Lux-Pain, this happens to Yui after Mako dies. She eventually tries to kill Tanaka as revenge for Mako's death.
In Draw With Me, the boy tries to get through the unbreakable (instantly repairing) glass and loses his hand for it. And then the girl cuts off her own hand to give to him to use to draw. (It Makes Sense in Context.)
Neomutant from TOME became a hacker in TOME just so he can protect his obsession, Flamegirl, from her actual Love Interest, Alpha. This help is nether needed or wanted by nether the girl or the love interest. He has also been in pursuit of her for an entire year, and is seen as being extremely 'dense', as well as selfish, when in regards to Flamegirl. To the point of attacking her love interest within two seconds of being revealed.
Oasis from Sluggy Freelance cranks this trope up to 11 until she finally winds up in a mental institution.
She's not gotten any better since leaving either. Sure, she had a point where she managed to level out - only to lose it again when her sensei was killed in front of her eyes. At this point, only death will save her.
A more humourous version of this showed up when Gwyn used a Love Potion...and apparently there are problems when it comes in contact with alcohol...
In The Dreamer, Alan infiltrates Gen. Howe's ship just to rescue Beatrice.
Vole may be big and mad, but he wasn't born yesterday, so during the Big Damn Kiss he didn't even try to intervene with his Ax-Crazy act:
Violetta: And here I kept expecting you to attack him. Vole: Dun be schtupid. She vould rip my fangs out.
Gil has a tendancy towards this trope, especially if he believes someone he loves is dead or missing. When he first thought Agatha was dead, he spent most of his time in The Madness Place. Losing Mechanicsburg with everyone he cares about inside has apparently driven him over the edge. He remains awake for weeks, once again constantly in The Madness Place, resulting in dark circles around his eyes, zombie-like look and irrational, violent behaviour.
Gunnerkrigg Court has a sentient cruise ship that holds Court Students hostage and wants to use Zimmy's powers to become a living thing to win the heart of Lindsey.
El Goonish Shive got Melissa, Unlucky Childhood Friend of Justin. Who told her he isn't attracted to her because he's gay. So she shared this grief with her rumour-mongering sister and everything quickly rolled downhill from there. She had fits of delusion that she could seduce Justin and revert the break if she tried harder — until he couldn't stand hearing her name. Sometimes managed to Dope Slap herself out of this, got another boyfriend, but... still continued to slip into this. They seem to become able to interact normally only after facing a bigger and more immediate problem together.
I've had my car stereo rigged to play "Making Love" out of nothing at all. I've received more drunk dialing more than anyone who ever dated Charlie Sheen. And I've had live bunnies airdropped into my house.
In return, The Nostalgia Chick keeps going further into insanity (and she wasn't exactly all there anyway) for Todd. On Facebook, she's even willing to have sex with his corpse.
The Maximal Silverbolt in Transformers: Beast Wars, despite being as heroic and noble as they come, did some highly illogical things for the love of the Predacon Blackarachnia, mainly because of the aforementioned heroism and nobility. Of course, in the end he was right about her, but it was foolish at the time, and he was punished for it. In this case, the other Maximals thought love had made him crazy, when in fact he just had some insight.
All over the place in Hey Arnold!. Besides Helga's complete obsession with Arnold, whenever Arnold is around Ruth (and later, Lila), he ends up acting very nuts indeed.
Camp Lazlo: Patsy lies to Lazlo that she is a professional snake hunter who knows Kung Fu. Lazlo believes her, until they end up running from a (tiny, cute) snake and are cornered. Patsy confesses to having lied, and Lazlo asks why.
Patsy: Because love makes us do crazy things! Lazlo: What?
Galaxy Rangers: Zach Foxx is normally The Stoic, a by-the-book contrast to the more "colorful" crew he's commanding. That is, until the Queen put his comatose wife near death with her "dream machine" stunt. Queue The Captain breaking into a high-security facility, holding a technician at gunpoint, and impulsively resigning his commission to embark on a suicide run. Of course, the Mind Rape aspect of that machine didn't help matters...
Jérémie Belpois. To put it bluntly, he willingly puts his entire world on the brink of malevolent A.I. apocalypse just about every day for the sake of maintaining a relationship with Aelita.
In "The Chips Are Down", when Ulrich finds out that Yumi may have to move to Japan due to financial issues, he memorizes the day's winning lottery numbers, reverses time, fills out a lottery ticket, and hands it to her family.
Despite what one might think, it's more of an Informed Attribute with William Dunbar. Around Yumi he's more of a Stalker with a Crush — about the worst he's done (in regards to their relationship) is follow her home to try and kiss her. He does, however, love to brag about how love makes him crazy — "totally insane", in fact — and he was expelled from his previous school for putting up poster-sized copies of love letters everywhere (including on his principal's car).
"Kaboom and Kabust" includes an explosive Falling in Love Montage between Rico and his newly-discovered enabler King Julien. His permissiveness whips Rico into an increasingly wild frenzy, until it's all the other penguins can do to contain his destructive rampage to part of the zoo.
In "Hello, Dollface", his beloved Ms. Perky doll gets a voice chip, and he does everything she says... to the point of becoming a hippie, much to Skipper's horror.
Kick Buttowski gives us Jackie... aptly nicknamed "Wacky Jackie" by many of the characters on the show.
In the Teen Titans Go! episode "The Date", this is very clearly the case with Robin in regards to Starfire. Nicely lampshaded by the voice in Robin's head, who points out excactly what kind of crazy love is making him.
Although whether or not it actually qualifies as "love", most instances of a Stalker with a Crush can qualify as this.
Romantic love is in fact linked to high levels of dopamine. High levels of dopamine are directly related to symptoms of psychosis, i.e. delusional thinking and hallucinations. Love actually makes you crazy.
A study noted that the behaviour associated with the initial stages of romantic love is functionally indistinguishable with the behaviour associated with obsessive-compulsive disorder.
The Lighter Side of relationships that end up needing Restraining Orders fits under this. There's only so much bad poetry, unsolicited messages and overtures one can take before annoyance builds to level usually reserved for telemarketers and things that get stuck in your teeth without any floss handy.