What just fine said. It's not a deep dark secret, really. You don't have to divulge all right off the bat. When you know her a bit and the time is right, tell her matter-of-factly. If you make a big deal of it, she'll wonder what the big deal is. Remember, it's not YOU who's the crazy one, it's THEM!
Hey, this maybe helped clear something up for me. I, too, was asking how to divulge my past to people. I think the answer for me is to make that phone call to a counsellor that I've been thinking about making, and practice talking about it there, to someone who should be safe and non-judgemental.
Oh, and NO, don't go back when you've come this far, don't second guess yourself. You'll just find yourself back where you started from, ugh! Find another game to play, don't play theirs.