Wow. There's a couple people who fall into this category, LDs.
~The Stepfather. It's sad that the only things you remember from your childhood are the beatings and the "you'll never amount to anythings" and the "fuck that, that's stupids".
~The Ex-Best Friend. I put more than my fair share into that relationship when we were in college, and she shit all over that. After the friendship withered and died, many...MANY friends asked me how I held on so long. And I had no answer because I myself didn't even know. I relate this one to "battered wife" syndrome (I have seen it happen in both Sister Dreamer and Cousin (she lost sister status several weeks ago) Realist - you stay with someone who is obviously not good for you and you know that, but you stay because it's comfortable and you know what's going to happen, even though it's bad.
Yeah, they're pretty much it. I'm not going to add in the several boyfriends that broke my heart, because that happens, LDs. And I'm still a better person for it.
Heepwah, and be safe out there.