Leslie: You just do everything your boyfriend tells you to do? Make any pancakes lately? Ann: He has two broken legs. Leslie: Yeah, and he's got three crutches. And one of them is you. And the other two are crutches.
Kazuya Aoi from Freezing is this for Stellizer. Before she met Kazuya she was a Broken Bird, unable to stand any physical contact and suffered constant torment from her half brother's sexual abuse. After meeting Kazuya she underwent massive Character Development and was able to face all of her problems and improved greatly for it. Now, her greatest fear is losing Kazuya, so much so that when her greatest fear manifest, it's in the form of Kazuya's sister, who was the closest person in Kazuya's life before her.
Played very close to literally in Serial Experiments Lain, in which Masami Eri attempts to talk Lain into loving him because, as he claims, no one else is capable of doing so—but in order to even exist, he not only needs Lain's affection, but also *requires* that Lain *worship* him as a God, and the most powerful being in the Universe. When Lain turns on him and criticizes his own manipulative logic in her Crowning Moment Of Awesome and renounces her belief that Eri has ever been a God and is only a narcissistic wannabe created by the real God, Eri literally just disappears, blinking out of existence completely, since by that point in the story, Lain was the last person left in the world to believe he was God.
In Kara no Kyoukai Mikiya Kokutou becomes this to most characters. Specially to Shiki over the course of the series, although she doesn't notice it until the final moments of the last film. After she and Lio (who was very attached to Mikiya as well) mistake him for dead, their reactions go to the extremes. While Lio goes more Ax-Crazy than he already was, Shiki goes through a Tranquil Fury and murders Lio, the culprit, 7 times over in the space of a few seconds. She then falls over, and realizes that she really doesn't have any reason to get up. Then Mikiya then claws his way back to her.
Of course, keep in mind that Mikiya is explicitly characterised as a literal bodhisattva. The relationship between Shiki and Mikiya is one of the most complex possible, actually, since it mirrors the theoretical dynamic between Buddha (Mikiya) and Christ (Shiki).
Last Order to Accelerator from To Aru Majutsu no Index, his Morality Pet that catalyzed his Heel-Face Turn after his defeat at the hands of protagonist Kamijou Touma. Seeing how she is integral to the SISTERS network, she is also the embodiment of his redemption. Also, she gets kidnapped. A lot. The entire second half of Accelerator's story arc is his quest to save her, which involves turning on the city that raised him, him travelling through Siberia, facing off against Angels and spontaneously figuring out and using magic, something which usually would at least severely harm any weaker ESPer and definitely kill the stronger ones like Accelerator. He also is taken care of by Yoshikawa, who has a great effect on his mental health. And then there's Misaka Worst, a girl who is his crutch and he is hers in return. Their relationship is… entertaining….
Kaede from SHUFFLE!. As long as she can live with and take care of Rin, she's the nicest, gentlest person around. It's only when he starts shutting her out of his life that trouble starts. To her credit, she tries to keep it under control and feels shame when she can't. The difference between her and a regular Yandere is that she doesn't care how many girls are in Rin's life, as long as she's one of them.
During his time with the Hawks, Guts eventually became Griffith's crutch. Griffith trusted Guts with the seedier elements of his power plays and opened up to him more than anyone, even Casca. The downward spiral toward the Despair Event Horizon that would eventually result in Griffith becoming Femto started when Guts decided to leave the Band of the Hawk.
Casca also had shades of this when it came to her relationship with Griffith, since she had also seen a more vulnerable side to Griffith that no one else had seen and helped him through it. Griffith did not take it well when he found out that she and Guts had become an item, which was the final straw before his Despair Event Horizon.
In Kaguya Hime, Midori is very much this to Yui, who becomes a useless crying mess every time they're separated. Midori hates it. And you can probably interpret a lot of other pairs as having this dynamic (Akira as Mayu's, Kaede and Katsura as each other's, Miller as Nobuo's, Yu-Ling as Gao Li-shi's, etc)
Both Simon and Kamina, from Tengen Toppa Gurren Lagann are interesting examples, as they are both crutches for each other. Simon is competent, but too timid to live up to it. Kamina, meanwhile, knows how to inspire confidence, but can't do much by himself other then boast. For these reasons both believe they need the other to go on. After Kamina's death, Simon undergoes a Heroic BSOD, but eventually gets better.
"Listen up, Simon. Don't believe in yourself. Believe in me! Believe in me, who believes in you!"
Kamina: "Listen, Simon, never forget. Just believe in yourself! Not in the Simon that I believe in, not in the Kamina that you believe in, believe in the Simon... that believes in you!"
The least controversial interpretation of Nanoha and Fate's relationship in the Lyrical Nanoha franchise is that Nanoha serves as Fate's Living Emotional Crutch in the late first and most of the second season, following Precia's abuse and abandonment of Fate. Fate herself later serves as this to other characters, e.g. Erio. A recurring theme of the franchise is that while anyone can require an emotional crutch at some point, they will eventually be healed of their traumas and live a happy and satisfying life, if given enough warmth and care. And firepower.
Played straight for Eureka in Eureka Seven episodes 24 to 26. She is constantly in grief at Renton's absence and determined to see him to the point that she departed from Gekko behind everyone's back, including the three kids, to find Renton. She was finally emotionally at ease when she was reunited with Renton.
Also, Anemone starts off as a violently psychotic Tyke Bomb, but grows much stabler in the presence of her handler/guardian Dominic. Late in the series, he manages to restore her sanity completely through the Power of Love.
This is essentially stated to be the case with Hawkeye and Mustang in Fullmetal Alchemist. When she's told that he's dead, she loses the will to live. Later, when he threatens to be consumed by his own desire for revenge, she - fulfilling the oath she made before the start of the series - prepares to shoot him; the fact that she intends to kill herself afterward keeps him from crossing his Moral Event Horizon. Later still, when she's on the brink of death, he begs her not to die and leave him alone. They're an unfortunate case of Love Hurts, but they'd still rather be together.
The Elric brothers are also a form of this for one another.
On the villainous side, there's Lust and Gluttony. Considering how Gluttony's a literal bottomless pit who only cares about his next meal, it says a lot how he listens to Lust and misses her, especially after she dies.
Light to Misa in Death Note (whether he wants to be or not).
In Puella Magi Madoka Magica Madoka Kaname is basically the only reason Homura Akemi keeps going. She also sort of acts as this for Sayaka, at least at first.
Oriko and Kirika, of Puella Magi Oriko Magica are basically two crutches leaning against each other. The former is the town pariah, and a Knight Templar who becomes increasingly conscious of the consequences of her actions, while the latter was antisocial even before being warped by her wish to the point of psychological dependency. Neither one seems able to survive without the other, happily risking their lives for the other's sake and no one else's, and neither seems to have any real friends outside of the other. The last scene of the manga shows this trope almost literally, with Kirika promising to shoulder half the burden of Oriko's guilt as they pass into the afterlife holding hands.
In Saiyuki the four main characters are arguably this to each other, as due to their pasts no one in the group functions at all correctly when they don't have the others to fall back on. This was best demonstrated when Gojyo left the party and things started going wrong almost immediately. More specifically though, Goku is Sanzo's (before he met him, he was emotionally dead) and Gojyo is Hakkai's. Both those relationships work the other way around as well, though Gojyo and Goku have much less volatile personalities so it isn't as apparent... Though it could be argued that without Sanzo, Goku becomes Seiten Taisen, and you don't get much more volatile than that.
Yu-Gi-Oh!: Earlier on, when Yugi and the Other Yugi are still extremely dependent on each other, Dark Yugi can really only "sense" the difference between right and wrong when he's with Yugi. So when the Orichalcos arc rolls around and Yugi's gone for a while...
In Yu Gi Oh Gx, Johan quickly becomes this for Judai in season 3. When Judai starts questioning himself and his motives for dueling, he opens up to Johan and ends up latching on him emotionally, even to the point of obsession (more details on that here). So when Johan gets left behind in the other dimension, the second half is almost entirely devoted to Judai's search for him (and his other friends hesitatingly coming along). His obsession leads to his friends getting captured and killed.
In Tiger & Bunny, Kotetsu eventually becomes Barnaby's Only Friend and confidant. It's because of his influence that Barnaby is able to adjust to having any sort of life after spending twenty years socially withdrawn and preoccupied with revenge. According to the creators, if Kotetsu had actually died in the final episodes, Barnaby never would have recovered.
In Axis Powers Hetalia Russia is normally an Ax-CrazyStepford Smiler. It's also hinted that Russia has feelings for his "favorite" Lithuania. Additionally if you ask the fandom, Lithuania is the only one who can keep Russia relatively sane.
Also, Russia truly loves his older sister Ukraine as much as his insanity lets him.
Germany for Italy, with the latter having fits of panic and depression whenever it's even hinted that Germany might stop being friends with him.
It's also likely that North Italy is one for Germany, as he mentions that Italy is one of the first friends he has had.
In School Days, Setsuna is this to Sekai. Setsuna knows it clealy, too; hence why she wants her to be with Makoto, so he can protect her because she's soon moving abroads and doesn't want Sekai to be all alone.
And Makoto is one for Kotonoha. When she found out that he was cheating on her, poor Kotonoha started falling into denial and despair.
In No6 it's hinted that Sion and Nezumi are this for each other. Nezumi for Sion especially. Take for example Sion's reaction to a guy almost killing Nezumi in episode 10.
Pandora Hearts: Elliot to Leo. Leo by far appears to take Elliot's death the hardest, blaming himself entirely for Elliot's death and losing his sanity in the days that follow. Elliot's also the only reason that Leo was even friends with Oz with Leo stating to Oz that now that Elliot is dead there's no reason for them to be friends anymore but rather enemies.
Alice to Oz. Oz goes into Love Makes You Crazy mode over Alice when he thinks she died and when she's feeling pain.
Oz for Gil. Big time. Also, Gil for Vincent. Though sometimes even Gil isn't enough to rein in Vincent's Ax-Crazy tendencies but its implied he would go completely and irreversibly Ax-Crazy if Gil ever died.
In Naruto we have Itachi being the Living Emotional Crutch for Sasuke with Sasuke not realizing it until Itachi dies and Sasuke learns that Itachi had done everything to protect him in an HORRIBLY convoluted way; he then goes mad with grief and has a huge moment of Sanity Slippage.
It's implied that Orochimaru was this for Kabuto.
Rin. Oh, dear lord, just Rin. She is not only a crutch for one, but two. She was Obito's entire reason for living, and also the only one who keeps Kakashi's mental health together out of a promise he made with Obito. When she dies, everything goes to hell for both boys. Obito becomes a psychotic terrorist hell-bent on an Assimilation Plot, Kakashi becomes a mentally damaged person whose sanity is barely hanging on.
Akio and Anthy are a dark example for each other— they manipulate and betray everyone besides each other because they're too afraid to live any other way. Their relationship isn't portrayed as healthy or pleasant for either of them (and in Anthy's case, it's clearly abusive.
In Ranma ½, although neither would admit it both Akane and Ranma are this to each other. Case in point, when he thought Akane had died Ranma went into a Heroic BSOD so bad that he only came out of it when he learned that Akane was still alive.
In Bleach, Ichigo is this to Orihime and Orihime is this to her brother Sora. For Orihime, her feelings for him are at first a cause of pain, and later a reason for self-improvement.
Every single one of Ichigo's friends and relatives is this for him, to the point that when his sisters and human friends were brainwashed by Tsukishima and turned against him, Ichigo fell in despair.
Lina from Cyborg 009 is this for Phil, despite his protests. When she's thrown into the Bad Future alongside Joe/the titular 009, Phil is devastated to the point of an Heroic BSOD, and Mai lampshades the trope by saying that without Lina, the child simply will NOT survive.
Hatori serves as one to Chiaki in Sekai Ichi Hatsukoi. Despite their personality types being reversed, Chiaki is unable to function without Hatori who has been taking care of him all of his life. Without Hatori by his side, Chiaki loses the will to do anything. And Hatori technically takes advantage of this by brutally raping his best friend. The dependancy is so strong that Chiaki is willing to ignore what happened to him just so Hatori will stay by his side. Naturally, this dependancy is shown to actually be more harmful than good.
Tsuna is this for Gokudera in Katekyo Hitman Reborn!. He reacted quite fiercely to learning Tsuna died and was the only one to visit his grave and did it quite often too.
This is the main reason Chrome Dokuro is Willfully Weak. She loves to rely on Mukuro.
In the beginning of Saikano Chise is acting as Shuuji's crutch. By the end, Shuuji is the crutch to an emotionally destroyed Chise.
Shinji's relationship to Kaworu has some echoes of this in the original Neon Genesis Evangelion, but it doesn't become a full-fledged example until Rebuild of Evangelion. In Rebuild 3.0, Kaworu ends up becoming Shinji's source of emotional stability and Only Friend, since nearly everyone else is either hostile or apathetic towards Shinji due to him causing Third Impact.
Eren is one to Mikasa: as he saved her from the people who murdered her biological family and is the only one of her loving adopted family left, she's deeply attached to him and even joins the military solely to protect him (despite her status as The Gift). Needless to say, she has more than one massive (but tranquil) Freak Out after she thinks something bad has happened to him.
Krista being one to Ymir is a darker example: Ymir is completely willing to side with the villains and take away Krista's future if it means she can have her to herself.
Kaori is one of these to Tetsuo from AKIRA, and is the one person keeping him from losing his mind completely. In the anime, she dies horribly when she's engulfed by the...thing that Tetsuo has become after losing control of his powers. In the manga, she's gunned down by Tetsuo's treacherous lieutenant.
Yukiteru for Yuno in Future Diary. One reason Yukiteru continues a relationship with her as the series goes on, despite her psychosis, is the fact that she is noticeably more stable and calm when she's with him, and he believes he can help her.
In Lying Mii-kun and Broken Maa-chan: Precious Lies, the titular characters are each others' crutches. The horrific ordeal they endured together in childhood screwed them up very badly, and their relationship is the only thing that lets them maintain even a semblance of sanity. As messed up as they are, the third kidnapped child aka the real "Mii-kun" is even more broken. The protagonist wonders if real!Mii-kun would have been less screwed up if he had remembered Maa-chan.
Exploited in Watchmen, where The Government employs young women (Janey Slater and later, Laurie Juspeczyk) as Living Emotional Crutches for the Physical God Dr. Manhattan, realizing that this is pretty much the only thing that can preserve the last shreds of humanity within him (and also incidentally, keep him on the planet and working for the right people). True enough, as soon as Laurie dumps him, Dr. Manhattan moves to Mars with no intent of ever visiting humanity again. And it's Laurie again who manages to renew his interest in humanity and come back to Earth, however briefly.
In A Growing Affection, Naruto becomes this for Hinata. When he is around (physically or spiritually), she is able to stand up for herself. When he's not, she is almost as much of a Shrinking Violet doormat was she was at the start of the story.
In Brainbent, Aradia to Sollux. He nearly hero-worships her, which is not unjustified — he has severe bipolar disorder, and she's one of the only people who has consistently stuck with him. She's also one of the reasons none of his suicide attempts have been successful. He tends to get very angry if anyone points out his dependency on her, but at the same time wonders if he's burdening her too much with his problems. She's pretty good at dealing with it, though, and says that she chose this and she can handle it, because he's her friend.
Apollo to Klavier in Dirty Sympathy, Klavier had been virtually isolated by both his fame and by his abusive lover so Apollo is the first person he got close to. When Klavier thought Apollo was killed, he nearly went over the Despair Event Horizon until he saw he was fine.
"Doctor, what is he going to do if...something ever really does happen to the Captain?" she asked hesitantly.
The question hung ominously in the air between them for a moment before McCoy finally managed to answer her.
"I don't know, Christine. I have my theories...but I'm in no rush to check them out. It's a question Jim and I don't ask, especially after something like this happens; we're afraid to find out the answer."
In the Facing The Future Series, it's revealed that Danny is this to Sam, who says that she can't live without him and that he's the only one who really makes her happy.
In A Charmed Life Ryuk becomes this for Light, helping him through his psychotic breakdowns.
Marlin to Dory in Finding Nemo. Normally she's a Cloudcuckoolander with all the long term memory of a sieve, but when she met up with Marlin on his quest to rescue his son, she could focus and remember the address of the dentist who kidnapped Nemo. When Marlin loses faith in finding Nemo, he leaves her to avoid remembering. Her speech pleading him to stay is one big Tear Jerker, as was her state when Nemo later finds her swimming to and fro trying desperately to remember what exactly she lost.
The 2007 Halloween (2007) plays Michael's obsession with Laurie this way, being the only person in his family he loved other than his dead mother. It doesn't end well.
The movie May had the eponymous May form a close relationship with Adam and ever so gingerly crawls out of her Shrinking Violet pot... only for things to Go Horribly Wrong when they later break up. She descends into full on horror-movieSerial Killer mode and proceeds to make the friend of her dreams from the most beautiful body parts of those around her.
Jacob is this, very much, to Bella during most of New Moon.
Patroclus can be interpreted as this for Achilles in The Iliad.
In the Novelization of Revenge of the Sith, Obi-Wan and Padme are both this to Anakin, to a point. A point which diminishes steadily as the story progresses and he turns increasingly to Palpatine; even at the beginning, he saw and sometimes resented their influence. Without them - after he kills Padme and drives Obi-Wan irrevocably away - he turns into Darth Vader.
Cathy was this for Heathcliff growing up amidst the abuse and prejudice of Wuthering Heights.
Karan of The Three Worlds Cycle has an excuse for this—half-breed characters in this setting are prone to serious psychological issues, and as a Heinz Hybrid she shouldn't even be functional. Her friend/love interest Llian somehow manages to stabilize her, and when she's separated from him, things go badly, to say the least.
Lucie in A Tale of Two Cities is the only thing between her father and solitary-confinement-induced insanity. He soon progresses from needing her presence to simply needing her happiness, but when Charles falls under the shadow of the guillotine, that kind of backfires.
I don't know when I've felt so rotten. Somehow I found myself moving about the room softly, as if there had been a death in the family. If I had anybody to talk to I should have talked in a whisper; in fact, when the telephone-bell rang I answered in such a sad, hushed voice that the fellow at the other end of the wire said "Halloa!" five times, thinking he hadn't got me.
The Beast from Beauty and the Beast (not the Disney version) tells Beauty that if she doesn't return to him within a set amount of time, he'll literally die of grief. When she stays just one day later, she receives a vision of him on the verge of death and rushes back to his side, at which point he promptly begins getting better even before she breaks his curse by agreeing to marry him.
Herald-Trainee Tylendel, to Vanyel, in The Last Herald-Mage trilogy. He becomes Van's first and greatest love and the only one he can trust. 'Lendel does nothing to discourage this dependence, which is why things start to go south when his own sanity begins to slip. And then it gets worse...
On the other hand, there are milder examples in some Lifebonded pairs, where a Herald with a slightly broody personality and a strong Gift bonds with another who is less Gifted but more stable, and this is treated as a good thing.
The Dresden Files has a supernatural variation: White Court vampireThomas Raith has a girlfriend who is schizophrenic and prone to dangerous mood swings. By feeding off her excess emotions, he allows her to be fully functional without the side-effects of medication. When separated from him for too long, her emotional instability returns and she becomes dangerous to herself and others.
At the beginning of The Hunger Games, Katniss' sister Prim is her Crutch. By the end of the series, Peeta pretty much replaces her.
Rosethorn is this for her student, Briar, in Circle of Magic. As of Battle Magic, it's clear that he is one for her as well: she very nearly breaks down completely when she realises that he's been injured. Although she's generally better at hiding it.
Archie Goodwin functions as something like this for Nero Wolfe; as Wolfe's personal assistant, Archie's pretty much the only reason Wolfe's carefully structured life functions as smoothly as it does, but he's also Wolfe's conscience when he feels Wolfe has crossed the line, and his snarky attitude works to motivate Wolfe into accepting work despite his laziness, preventing him from stagnating. Accordingly, despite the frequent tension between them Archie is one of the only people — if not the only person — Wolfe ever expresses any genuine regard for.
To a lesser extent, Wolfe also returns the favour for Archie; most notably, in one novel Wolfe disappears without trace for several months, forcing Archie to open his own detective agency. He makes a point of noting that while he made more money than he ever made working for Wolfe, he found the work a lot less interesting.
Live Action TV
Buffy the Vampire Slayer: Giles for Buffy in the first half of Season 6. Giles eventually leaves to force her to become independent.
In Smallville, Chloe is this to Davis during season eight. Might be one towards Clark on one of his worst days.
Simon to his sister River in Firefly. It's very much reciprocated, as the movie Serenity shows us exactly how dangerous River can get when Simon's life is threatened.
River Tam: You take care of me, Simon. You've always taken care of me. My turn.
Every person on Serenity to Mal. They each represent some emotional aspect or part of his life he's become dissociated from.
Peter to Walter in Fringe. Peter can somewhat focus Walter, calm him down, and ground him in reality. However, Peter is very critical of Walter (and oddly overprotective), leading to bouts between them or Olivia.
Sam is this for Dean in Supernatural. The boys definitely have their troubles when they are together, but when Sam is gone, Dean falls apart. Case in point: "All Hell Breaks Loose Part 2." Dean is also this for Sam to a slightly lesser extent; when Dean went to Hell, Sam practically destroyed himself (and probably would have ended up killing himself had Ruby not stepped in). It's also heavily implied that in season 8, Sam slipped into a fantasy world when he lost Dean.
Zachariah: You know Sam and Dean Winchester are psychotically, irrationally, erotically co-dependent on each other, right?
Sam has always been a bit more independent than his brother, and appeared to learn a lesson from Seasons 3, 4, and 8 (the various times he went berserk from losing Dean, whether by killing, addiction or nervous breakdown), but this has been taken to an ugly extreme with Dean in Season 9- while not the cause of Dean's Dark Arc, his conviction that Sam doesn't love him has given him little incentive to even try to fight the violent impulses of the MOC/First Blade. At the same time, when he does go Kill Crazy, Sam seems to be the only one able to talk him down.
Wild Bill Hickock is one for Calamity Jane in Deadwood. Then he gets shot in the back of the head, and she goes on a drunken binge that lasts about a year.
In The Vampire Diaries, Stefan Salvatore employed this role frequently in the series with more than one character. He largely fulfilled this role for his older brother Damon Salvatore and formerly Elena Gilbert. In Elena's case, he was her crutch that caused her to be glad to be alive after the death of her parents, but her dependence on him gradually lessened in that aspect until he disappeared altogether when she fell in love with Damon. However, his influence on Damon remained, shown in how he would become extremely violent, impulsive, and bitter without Stefan around him.
Later in the series, Damon replaces Stefan's role for Elena. After she was turned into a vampire, Elena was taught to enjoy the perks of her new transformation and feel happiness again. Elena even admitted, in her love confession to Damon, that he was one that made her feel most alive.
Elena: I'm not sorry that I met you. I'm not sorry that knowing you has made me question everything, that in death you're the one that made me feel most alive. You've been a terrible person. You've made all the wrong choices and out of the choices I have made, this will prove to be the worst one. But I'm not sorry that I'm in love with you! I love you, Damon. I love you.
Yet, unexpectedly, Stefan takes up this aspect again in the extreme for his sometimes lover, Katherine Pierce. After she's dying of old age due to the loss of The Cure, she re-connects with Stefan when he stopped her from killing herself. As her impending death draws closer, Katherine latches on to Stefan's compassion and falls in love with him all over again. She's becomes surprisingly dependent on him, admitting to Nadia that Stefan is the only reason she wants to live.
Nadia: I see. So when you were asking about forgiveness, you were talking about him. Not me.
Katherine: Maybe I don't want to die a sad, lonely 538-year old. If I have to bow out, knowing Stefan still cares might not be the worst way to go.
On Teen Wolf Scott McCall is this for Derek Hale, Stiles Stilinski and Allison Argent.
Merlin is this for Arthur on Merlin. Without Merlin and his influence, it's been shown that Arthur cannot function that well on his own.
Gaius is also this for Merlin.
Rose was this to the Doctor in Doctor Who during seasons one and two of the new series. When they were separated the Doctor spent the next season depressed and implicitly suicidal. The last time we saw the Tenth Doctor genuinely happy for any extended period of time was during season two.
All the companions, to a certain extent. They work as a combination of friendship, a Morality Chain, and helping the Doctor see the beauty of the universe again. In the new series, although he loved Rose, he was just as disappointed when Martha left him, completely devastated when Donna's memory was wiped, and became a virtual recluse when he lost Amy and Rory (not to mention going into pure fury when Amy was kidnapped). Even in the classic series, the death of Adric tore him apart. In fact, the Doctor seems to be dependent on these crutches, but unlike many of the other examples on this page, is doomed to outlive all of them.
This holds especially true for the Doctor and Lucie Miller after Orbis.
On Torchwood Jack Harkness emulates the Doctor by also assembling his own teams of people who help to ground him and give him purpose. He is virtually immortal and without companionship tends to go into bouts of depression and self-destruction.
The X-Files: Mulder and Scully are this for each other. In the beginning, it was more that Scully was an emotional crutch for Mulder, who is introduced as brilliant but troubled. As time goes on, however, it becomes just as hard for Scully to function without Mulder as it is the other way around. There isn't really a dark side to this aspect of their relationship; rather than trying to keep Scully around forever, Mulder urges her at several moments in the series to leave him, to have a normal life away from his quest and problems. They are each other's Berserk Button.
In fact, it's kind of the opposite of being played darkly; once Mulder seems to have decided once and for all that Scully really is more important to him than his rather self-destructive obsession with his quest, he's able to resolve a lot of his personal issues and becomes a lot more stable.
During Scully's abduction in Season 2, Mulder essentially falls apart. When offered a hotel room in "3" while working a case, he tells the local investigator that it wouldn't be needed because "I don't sleep anymore." He also wears Scully's cross around his neck. When she is returned in "One Breath", he bursts into the hospital and demands explanations as to how she got here, having to be forcefully dragged out by security.
This works the other way around, too. When Mulder is abducted in Season 8, Scully goes almost immediately from her hospital room to launching a non-FBI sanctioned search for him, despite the fact she's pregnant. When he's returned dead, Scully has her own version of a Heroic BSOD.
It becomes even more striking when Doggett and Reyes are introduced into the series to replace Mulder and Scully on the X-Files. They clearly have feelings for each other (in season 9, anyway), but aren't nearly as dependent on each other as Mulder and Scully.
In Monk, Sharona is this for Adrian, until she leaves the show; the very next episode shows him finding her replacement, who continues in this role for the rest of the series. It's heavily implied that neither of them are a patch on his late wife Trudy, around whom he was genuinely happy and almost neurosis-free; her murder caused the Sanity Slippage that turned him into a Defective Detective.
In Degrassi, when Ellie starts dating Sean, she insists on bringing her Pet Homosexual Marco with her on their dates, and he is explicitly called her security blanket. This is largely because she's never been in a real relationship before, and had only been someone's beard up till then.
Inspector Lynley and his partner, Sergeant Havers. They are both incredibly screwed-up people, but over the course of the show regain something resembling normal emotional stability because they happen to balance each other perfectly. Separate them again, and the results aren't pretty (although not as bad as they were before they met each other, thanks to a healthy dose of character development).
In Elementary, Joan Watson is this to Sherlock Holmes, and he flat out admits this to her and his brother when they are in the imminence of being apart.
Despite their bickering, Vince is Howard's crutch in The Mighty Boosh. In Tundra, when Howard thought Vince had died, his instant reaction was to try to kill himself. When Vince was revealed to be alive, Howard was so happy he made a dramatic love confession.
As with the above examples, in Sherlock, Sherlock depends on John to be there for him and honestly,John needs him too.
I don't wanna be a crutch, one step away from down
A lot of the relationships in Peanuts are arguably this, since the characters are brimful of neurosis. (Just temporarily take someone out of the picture and place your bets on who will have a breakdown. Someone always does.) Even Linus' blanket is an example, as it often takes on a life of its own.
Many of the more poignant Calvin and Hobbes stories imply this. In spite of bullies and all sorts of other bad things in his life, Calvin will always have his best friend Hobbes.
Enobarbus: Why, then, we kill all our women. We see how mortal an unkindness is to them. If they suffer our departure, death’s the word.
Antony has quite the opposite opinion, at least for Cleopatra.
In Company, the lyrics of What Would We Do Without You? indicate that Bobby is this to his married friends, or at least to their marriages.
What would we do without you?
How would we ever get through?
Should there be a marital squabble,
Be there with the glue.
Your player character in Dragon Age: Origins is everyone's emotional crutch, but bonus points go to Zevran, who goes utterly to pieces if he loves and loses you, and whose shot at redemption hinges on whether you build up a strong relationship with him or not and Alistair (who counts on you to lead the team, deal with his parental issues and with a little luck, follows your leadership example and become a good king. Most characters will show development and stop using you as an emotional crutch once you've slain their personal demons/dragons...
In Dragon Age II, Hawke fulfills this for a Friendship path Anders and Merrill. Fenris has elements of this as well. Over the course of the seven years the game covers, Hawke can help them work through their troubled pasts and personal issues but will be unable to save Anders from crossing the Moral Event Horizon. On the Rivalry path, the companions take a more proactive stance in their life, and rely less upon Hawke. Whether this is a good thing is a personal matter.
Anderson orders Joker to act as this for Shepard in Mass Effect 3 because once the Reapers show up, Shepard is under greater stress in his/her resting state than s/he's ever been in his/her life.
Many of the interactions in the game and dialogue options can have Shepard reveal that s/he is relying just as closely on some of his/her closest teammates/friends, especially Liara, Tali, and Garrus to keep it together.
Shepard: There is no Shepard without Vakarian.
In Blaze Union, Siskier was the first person to befriend Garlot when they were little kids, and worked hard to ensure that he had a place to enjoy himself and act his age so that his father's abuse wouldn't destroy him completely. Even now, he sees her as something of a mother figure, and relies on her support whenever he has doubts. In the route where she is killed, Garlot nearly goes berserk on the spot, with the only thing stopping him being the seal on his powers, which cuts his rampage short as soon as it starts. He develops severe PTSD afterward, his personality becoming quite a bit harsher, although the rest of his True Companions still serve in this role. In Yggdra Union, he really does go berserk after every single one of them is killed.
In Pokemon Mystery Dungeon Explorers of Time/Darkness, you are one for your partner, to the extent that after you are removed from time and space, the god of time sees fit to make an unstable paradox by putting you back rather than have your partner sad.
.hack//G.U. had Endrance, whose entire world reflects around Mia and only Mia while everything and everyone else were too ugly, weak and boring to care for. After Haseo reveals his cat as an AIDA and destroys her while fishing for Endrance to get back on his feet, Haseo becomes this for Endrance instead. However, his views on the rest of existence slowly become more positive in doing so. Also do note, Endrance is played by Elk's player. His dependancy on Mia goes all the way back to the original games, though not to this extent, and possibly put Kite in this role After Mia awakened as the Phase Macha
In Solatorobo, Elh becomes this to Red when he starts Hearing Voices, providing another voice to focus on instead of the one trying to convince him to kill everyone.
Fire Emblem Tellius has Ike as one to Soren due to treating him like a person when everyone else treated him like he didn't deserve to exist, and saving his life as a child. Ike is almost always on-screen when Soren smiles, is the only one Soren shows a softer side to, and is the only one Soren seems to actually care about as more than just another soldier or formal position-holder.
Although it's not entirely obvious from the beginning, Mia's crutch in Duel Savior Destiny is her brother. Without him, she becomes deeply unstable and jealous culminating in her attempting to kill her allies in her own route. She sorta gets better. Well, she gets to have her brother around all the time anyway, meaning she won't go all crazy again.
In Halo 4, the Master Chief gives Cortana hope and the will to fight against her impending insanity/death due to rampancy. At the end, after her Heroic Sacrifice, John-117 reveals that her partnership with him was allowing him to hold onto his humanity.
Tales of Graces has Sophie acting as this to resident self depreciating Asbel (who thinks he's a Failure Hero). By being the father figure she needs, she gives him a reason to not wallow in guilt and self-pity
In Final Fantasy XIII-2, it's heavily implied that Hope feels this way about the whole group (including Serah), but it's most noticable when he mentions Lightning, Fang or Vanille. Given his implied feelings of abandonment after his mother left him to fight the Purge (she had his safety in mind), and how much of a motherly figure the women in the previous game (especially Lightning) became to him, it's understandable.
The fact that Serah, Snow and Sazh all disappeared (on their own adventures to find Lightning and into a paradox, respectively) after the loss of the aforementioned four sure as hell made it worse.
Amy has the main character, Lana. This is Truth in Television; autistic people almost universally fit this trope.
Dead or Alive: Ayane's relationships with Hayate and Genra are indicated to be as such in Dimensions. When Genra makes a Face-Heel Turn and she offends Hayate during an argument over Kasumi, Ayane ends up thinking that Hayate hates her now and is so distraught over it that she almost kills herself.
Phoenix Wright: Ace Attorney: Justice for All. Adrian Andrews suffers from an intentionally overcompensated for and totally-played-straight Dependent Personality Disorder. Initially appearing as a self-contained narcissist who needs no one and prefers being by herself, it is later revealed she is actually the exact opposite in hiding and willing to do literally anything to not be found out. Her codependent pathology is so severe, in fact, that it is eventually discovered that she attempted suicide after the death of the person she pathologically idolized and lived exclusively for: Celeste Inpax. In an attempt to hide this fact, she forms a relationship with Franziska von Karma to protect herself from needing to reveal her true nature. Andrews, naturally, clings to Franziska like a terrified and helpless child, doing everything she says without any thought of her own needs.Some fans (of both genders) have interpreted all of Andrews' relationships as Les Yay, but it's more likely she suffers from extremely severe depression with her accompanying pathological neediness and paralyzingly low self-esteem.
In Katawa Shoujo, Shizune is one for Misha, as seen in her route.
Hisao becomes one for more than one of the girls in their respective routes. Also viceversa, as in Lilly's route he comes to emotionally rely on her. Deconstructed in Hanako's route: he aims to become this to Hanako so he can protect her, which will end up alienating her if you keep it up.
Also, Emi keeps people at arm's reach to avert having someone become this. And specially, to not suffer if she loses someone else she loves, as happened with her father, who died in the accident that took her legs.
Ryoserves as this for Hibiki in Lux-Pain. Hibiki crossed the Despair Event Horizon in his backstory and it was Ryo (and the nurse Honoka that brought him back to almost complete health...only for it to shatter when Ryo gets a new, beautiful assistant who Hibiki gets jealous of as she serves as a better caretaker of his best friend than him. And of course, Ryo being unaware of his best friend's feelings also makes him completely lose it. Once you beat the game again and you get the cutscene where Ryo tells him not to disappear on him again, you can see that Ryo is what keeps Hibiki from completely going insane. Ironically the normal ending implies that they serve as an emotional crutch to each other as in the normal ending when Hibiki is killed by a crazed Honoka, you don't get to talk to Ryo anymore as the game implies he locked himself in the library shocked that he lost the last person that was important to him.
Little Busters!: Kyousuke (and to a lesser extent, Kengo and Masato) are this for Riki and Rin, who are so shy and fearful of strangers or so passive and worried about the outside world respectively that they are very dependent on them. In fact, the main driver of the plot is Kyousuke's attempts to break them away from this, as a bus they were travelling in crashed, leaving everyone but Riki and Rin with fatal injuries, and Kyousuke knew they couldn't survive on their own.
Like its anime adaptation listed above, School Days has multiple examples. Makoto becomes this for Kotonoha, to the point that she is homicidally insane if they're not together. On a less batshit crazy level, Setsuna fills this role for Sekai; the reason Setsuna is pushing Makoto towards Sekai so hard is to get him to fulfill this role for Sekai, since Setsuna is about to move to France.
Subverted in Saya no Uta. The main character suffers from a severe case of agnosia that causes everything he sees, hears, touches, etc to be utterly replusive (everything's covered in or made out of Meat Moss, people are disgusting amorphous creatures who bellow nigh-unintelligibly at him, etc.) Saya, the only person who appears normal to him, quickly becomes his only reason to keep living. Unfortunately, having an Eldritch Abomination as an emotional crutch doesn't exactly do wonders to your sanity, and while he may be happy in his madness, he also ruins the lives of everyone around him in spectacularly horrific ways.
Web Comics/Web Original
In Drowtales, Ariel has this relationship with Faen, being the first person she called friend. Also suggested to go the other way as well, since Faen is an unstable empath who has difficulty relating to people.
Fox Maharassa was a Living Emotional Crutch to boyfriend/best friend Collin throughout most of Friendly Hostility. When Fox loses the Emotional Crutch status, the relationship falls apart, although this is arguably only one of the factors that resulted in the Downer Ending.
Iriana and Mille are this to each other in Ilivais X. Iriana literally has nobody else, as while she's decent enough to the male members of the team, she's still quite afraid of men. The only reason she avoids constantly searching for ways to die is because she wants to figure out exactly what she feels. Mille, on the other hand, is so used to being a one-night-stand object of lust that she feels utterly unloved, and is utterly obsessed with earning the love of someone who doesn't just want to sleep with her. Granted, she's far more capable of independence and will act on her own, but if separated from Iriana she shifts all of her thoughts to bringing them back together, and can't stand to keep away even after a brief period of being abused by her.
Zimmy literally cannot function without Gamma. Zimmy's powers leak out whenever Gamma falls asleep or is absent. This normally wouldn't be so bad...it's just Zimmy's powers consist of Reality Warping, which often sucks nearby other people into demented and twisted hallucinations.
In Homestuck, one of the four kinds of troll romance is moirallegiance, in which a relatively calm troll pacifies a dangerously hot-tempered one. There are several in-story examples.
Eridan and Feferi's relationship is practically a deconstruction of it. Feferi keeps Eridan's genocidal tendencies in check, but Eridan eventually wants to take things to a more intimate level. However, the chore of constantly keeping her moirail from killing off all the land-dwelling trolls has emotionally drained Feferi. Once they get into the Medium and she doesn't have to look after him anymore, Feferi tells him they can't be more than friends and splits with her newfound freedom. Later they seem to just barely be able to interact with each other, and and in the end, Eridan goes on a rampage, but before Feferi can run him through with the culling fork to stop him, he one shot kills her with White Magic of Hopelessness.
Black and White from Grey is... are this to each other. Black needs White around to be able to think clearly and White needs Black to bring color into his world. Their friends and family however, saw this as unhealthy which eventually lead to White leaving for 2 years
In the now defunct Loserz, Jodie does not take her two friends leaving her alone for other activities well at all. It only takes about a day or two apart from them for her to go insane and try to replace them with puppets.
Dan becomes this to Michael in Agents Of Cracked. According to Michael, if Dan left, "I'd get really sad - and then I'd die. Is that what you want?!"
Bittersweet Candy Bowl deconstructs this with Mike and Lucy's relationship. At the start of the series, she's extremely heavy on the Slap-Slap part of Slap-Slap-Kiss... but if anything happens to Mike that she's not inflicting, she breaks down. Mike is painfully aware of his LEC status, and secretly resents it — so much so that by the time Lucy's Character Development has made her less abusive and willing to admit her feelings, he rejects them, having been worn down into someone who's a lot less nice.
Tacoma for Donnie in Demo Reel. He loves Rebecca too, but whenever Tacoma's upset or sick, there's a suspiciously large amount of crying and cuddling going on.
Marten is this for Faye in Questionable Content; this is true, anyway, in the earlier parts of the comic. Character Development hit Faye, making her attachment to Marten vanish. It was difficult for both of them.
The Ren & Stimpy Show: It's implied that Stimpy is this to Ren, and that without Stimpy around Ren would become completely and irreversibly Ax-Crazy and overcome by loneliness.
It's more than implied. In the very first episode, Stimpy leaves Ren (temporarily). Ren falls to pieces within the first five minutes.
Appa and Katara serve as this to Aang, to some degree, particularly in regards to his grief over the annihilation of his people, the peaceful Air Nomads (Appa is his only remaining link to his past while Katara gives him hope for the future).
In "The Runaway" episode, it's hinted that Katara might serve as this to Sokka and even to Toph on some level.
In Rugrats Chuckie is this to his father Chaz. In one episode Chaz goes insane in a world where Chuckie doesn't exist.
Although considering that Chaz already lost his wife and that Chuckie is his child, this is very much justified. And heartbreaking.
Arnold for Helga on Hey Arnold!, for being nice to her when everyone else in her life was neglecting her, as is readily apparent in "Helga on the Couch".
PJ from Goof Troop is a more passive example of someone who needed help, but he acts depressed (apathetic, distant, and moping) in the first half of the pilot, and only starts to smile in the second when he's around Max. He even explicitly states that the day of fun he's had with Max is the only one he can remember ever having. His misery is highlighted repeatedly whenever their friendship is in danger. Though he may become less dependent on Max after finding a Love Interest in An Extremely Goofy Movie, it's unclear whether she won't just replace him, and it certainly doesn't take immediate effect: when Max threatens to transfer schools, PJ relapses from his Character Development.
In "Owls Well That Ends Well" fear that he would lose his status as her Number 1 Assistant temporarily made him a villain.
In "The Crystal Empire part 2" his greatest fear is revealed to be her revoking this status and casting him out of Ponyvile because she doesn't need him anymore.
In "Spike At Your Service" Twilight gave him the weekend off and he had nothing better to do than smell his feet.
Twilight Sparkle also revolves the majority of her life on the approval of Princess Celestia, her own greatest fear being her rejection. One instance implies Twilight may have gone completely insane without her and Spike's intervention.
Technically, every human has one in one way or another; it's more obvious in already broken cases, but it has been shown that everyone has a person they are especially attached to and would freak if they wouldn't exist. Pets, good friends, a Love Interest, children, or the local barkeep that they go to every night.
A large percentage of service dogs, whatever their primary purpose may be, also fufil this role for the humans that they're partnered with.
Then there are emotional support animals whose job is specifically to be a Living Emotional Crutch.
Then there is the unpleasant example of animal hoarders, who take this trope to the extreme at the expense of the poor animal's well-being.
Common in professions and situations where intense pressure bonds small groups of people. Small military units in intense combat; people in hostage situations; long-term law enforcement partnerships, etc.