I think you gave yourself the best advice : just work on being friends.
I think you'd just end up getting hurt again, seems like she's done some pretty hurtful things over the past however long to you broly. I can't pretend to understand the situation you're in. I just can't imagine if you did get back into a relationship with her that the trust would ever be the same or the feeling.
I don't think you can do that kind of thing or hurt someone that way if she truely did love you, just my two cents. I know you'll do whats best for you.