Edit -- a post slipped in while I was typing! I'll get to it.
Here's a vital bit of wisdom I discovered along the way....
(I read it in a book long ago. Can't remember which book, and only remember it as a paraphrase.)
How your friends treat you (and lovers, too) is how you treat yourself.
This sounds ridiculous on the face of it to many, but think about it. You keep them around. If they treat you badly? What does that say about how you treat yourself? You could walk away, right?