It sucks to live in the past, for whatever reason. I think the only thing I can say is an opinion, but DO NOT let what someone else did change the way you feel about this person. It's up to you to decide if she's different or not. Two things: Imagine it turned around, and her not giving you a chance because she's afraid to get burned. It sucks to be on that side of things, thinking that there could be something special if only he/she could see that you're not the same person that burned them before. And then there's the "what if" feelings. Are you prepared to reach a point in the future where you'll question what could have been? And the opportunity has passed. Most people don't get second chances when it comes to that stuff.
If it doesn't subside, I'd recommend finding a counselor or therapist where you can just unload all of those feelings and let it out to a third party, who may be able to give you advice. Counseling may be covered by your health insurance as well.
Fuck that, save your money! Just read through the last 86 pages and that will be all the therapy you need! And that's only a half-joke (if you have real issues, a mental health professional is a good start), because you'll find all sorts of insecurities and questions that persist in OUR heads. And that OUR is pretty damn collective. I think you'll find that a decently large cross-section of inter-personal relationship issues exists right here. Just read, and I can almost guarantee you'll find some perspective, and maybe some clarity.