Trust issues because of both of our pasts

I have been with my girlfriend for 10 months now and I am having trouble with insecurity. My relationships before her ended with the girl cheating on me twice. When my current girlfriend and I met, we discussed our pasts and she said that on her last field work summer (right before we met) she cheated on her then boyfriend of 4 years. She said that she knows what she did was wrong but it also helped he realize it was really over. It was going in a downward spiral for 2 years at that point. I am glad she was open and honest but now whenever other men talk to her and I see her being friendly it upsets me, and this summer she went to the same field work trip. She has told me many times that the last time was different and she would never do that to me but it only makes me feel better for a short amount of time. We love each other very much and she is the jealous type as well, but I am afraid that I might never get over this insecurity. I feel guilty as well because even though she is just as jealous as I am, she volunteers a lot of personal information, like the fact that she cheated before, passwords so I could check something for her over the phone. She seems to share the jealousy but not the trust issues. She says it might be because she was never cheated on to her knowledge and can sometimes be too trusting of people.

She never confessed to him what she did, and tells me that she feels more guilty about what it's doing to me now than what it could do to him if she told him.
Don't people who get away with things like that and never confess eventually repeat? If they can get over it and not have to be punished for it, couldn't that mean they might feel more comfortable doing it again?
How do you get over being cheated on in the past and then finding out that this amazing woman also did that to someone else not too long before dating you? How can you move past the paranoia about her dancing with other men, when dancing is what led to her cheating that night on her ex?