Sometimes, when the author wants it, or because the plot demands it, a character's heart is doomed to suffer: The loved one killed, the family mutilated, and so on until the character enters to a depressed state. This might be the hero, the vuillain or some random secondary character.
This trope can also come true when a character has some kind of ability to see someone's death and not being able to prevent it, or simply by being inmoral and seing everyone he cares about die.
Sometimes the plot-driven depression is accompanied with the fact that the character can't kill itself, making the suffering even worse.
Examples of this are found everywhere.
- Seen many times in Anne Rice's "Vampire Chronicles" being the best example the protagonist of "Interview of the Vampire": Louis, who lost his family and was in a depressive spiral of alcoholism, until Lestat came in and converted him. Now Louis is inmortal, but the fact is that he wanted to die, but now he thinks "he might be doomed because is a vampire" makes him think he'll go to hell when he dies, so he can't commit suicide. Poor old Louis spends his days feeling sorry for himself. He's got to be the lames vampire of the whole saga.
-Harry Potter: Almost everyone who fought alongside Harry in the Battle of Hogwarts at the en of The Deathly Hallows has to face a close death of a loved one or family member, being the very own Harry the biggest example, at lest at the middle of the battle when he thinks he is the reaon of all of the killing.
-The really "doomed to be an emo" character is, of course, Snape.
-In The Lord of The Rings cinematic Trilogy we watch the perfect love story of Arwen and Aragorn until Elrond points out the obvious with a sad profecy: "Aragorn will eventually die, and Arwen will be the forever young grieving widow" This makes her fall into depression until the end of the trilogy.
On TV series:
-The Vampire Diaries: Demon points out that the vampires have bigger emotions. Thus, Stefan who has always feeled guilty, now is a total and complety self blaming man, feeling sorry for the fact that he has killed countless people. His solution: Not to kill more people, then when proven wrong, kill more people, which makes the guilt even worse. Therefore, doomed to be forever and emo..