I can't say I've done that many horrible things to my characters.
The worst is probably what I did to Juliet in a tournament that became a real backstory. Her parents pretty much handed her over to a demon in order to protect her family's most prized possession. I think on top of her already rough childhood, that truly broke her last ties with her old life. She's never quite completely right even now, though. Hence why every once in a while she will feel the pull to cross to the other side. Recently she came very close to killing an innocent and I think she would've easily gone through with it had Elijah not been there to stop her. Very few things are keeping her anchored in the good side and sometimes I feel bad for her because every day is a struggle for her to continue to be a good person, and she continues to feel undeserving of the happiness in her life. I might have once or twice considered making her turn evil completely just to see what happens since she's been toeing the line for a long time now.
Freya is my other frequently suffering character, but most of the hardships in her life happened because of other people's doings. Watching Leto come back and Xavier deal with his leftover feelings for her, then losing Menefer and Xavier subsequently were really hard blows for her. I remember every post written in Xavier's absence was so painful and difficult, though I like to think this also lends to longer and more evocative posts. The only thing that I did myself to her was making the discovery that her foster parents were still alive after years of believing otherwise,
and they're living with the Magi,
and they don't want to come home (for her own protection). That felt like the ultimate betrayal for her and makes it difficult to reconcile her love and yearning to see them again with the feelings of deceit and hurt.
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Losing him was blue like I’d never known
Missing him was dark grey all alone
Forgetting him was like trying to know somebody you've never met
But loving him was red