Hi Gsx,
I imagine how hard that situation is on you.
I think Anxiousinfla is completely right about jumping from one relationship to another, and that you'de be getting yourself into troubles by doing it.
It would be very hard for things to work in that situation, even if she wants to get out of her present relationship it will probably take her some time to do that, people sometimes go back, break-up, go back, untill there's nothing more to go back to, and if you're already feeling down, being part of this would drag you down even more.
Be positive about that, if there's really something going on between you and her, chances will get better with time, not worse.
I think I understand you about being in a bad shape, maybe this is what you should think of for now, to get well again, to get the balance back, it seems that your self image is a bit low (I'm about your age, it seems to be the first age crisis, the 30's...).
This is something you can change, allthough it's not easy, you can start dealing with what makes you feel bad and holding you down, solve it or cope with the unsolveable, and get the good shape back. The pain you're used to hide, maybe work place wouldn't be the better one for you to show your feelings, but it would do you good to talk about it with someone, maybe do psycotherapy.
I feel I started changing things when i began doing psycotherapy and facing the past, by letting that pain go, everyday a little bit. Things will continue to hurt you deeply for some time, but at a certain moment you'll probably reach a point where the worse is gone, and that you just have to hang on for things to get better.
Maybe this sounds like the sort of positive thinking one gets in "self-help" books, the kind we don't believe when we're down, but the hopelessness feeling is the worse trick depression plays on you, so, think about the good things. The bad things in your way, the strength you use to handle the pain is enough for you to sort them out.
I hope you'll get better soon. The support I got here helped me, I hope it will help you as well.
lenny