Wow, went through this very same thing which all ended up in a big mess for me last summer. I know exactly how you feel, you know deep down what's going on and that it probably isn't right for you to take her back but the heart wants what it wants. You can't really change that part of it.
The advice I would give you is to tell her that she's screwed up too many times and it's never going to work out between you two. You don't have to be a prick, and if you care for her then you won't be. Just be honest. Then COMPLETELY cut her out of your life. It's probably the hardest thing I've ever had to do but I stopped emails, phone calls, threw out everything associated with her, etc. You'll still think about her a lot (if you're anything like me) but doing this will make it much easier on you. Know that it will be better for you.
I also took up some new sports, and so far I'd have to say rugby has been the best. Tonnes of guys who are always ready to giv'r which really helps a guy in your shoes. Lots of clubs, sports, activities to pick up with all your free time. Oh, and get ready to screw some ladies over (it's inevitable).
Several studies have investigated the relationship between intelligence and the degree of religious belief (excluding humanism), with most showing an inverse correlation between intelligence averages and the "importance of religion" to the testee.