I guess that depends on how much you care about someone...?
Usually when a relationship gets to this point, friend/lover/etc, and the relationship becomes negative I just cut that person out, if everything can't be worked out in some way.
I guess I look at this differently than a lot of people though... you can't help someone that won't help themselves, and if they aren't motivated to take care of themselves and their own life... then how can they help/care about someone else? I don't think anyone should sacrafice themselves for the sake of others.
And this line of though is how I, and my high morals, are prepertually single
So maybe it's not the best thing to ask me.
But generally, I learn what went wrong..and if it can't be fixed, I move on and try to learn from those mistakes. But that is something I do on every level, not just for relationships. I'm sort of cold for just cutting things out of my life, but so far I've been the better for doing so.