As much as you can, try to remember while you're going through this, while he's making your life as miserable as he can as his parting shot- that he's in a lot of pain. He wouldn't be treating you this way now if he was happy with himself, and he certainly will be doing his best to make it tough for you as you're leaving, but because he's hurting. It isn't really because he's an inherantly bad person, he's just hurting. I suspect the best thing you can hope for is that this might be the impetus for him to do what he needs to do (get therapy?, or whatever) to get his life together. Meanwhile, you can't keep sinking with him. But you know this.