Quote:
But if you can't work it out on yourself, DO NOT STAY IN THE RELATIONSHIP.
Very solid advice here. I missed this point in my response.
As to the OP question how to deal with this, yes the problem is common, and all it means is that you need to work on your inner game.
Personally, I would have more reservations dating a chick who has never cheated, or says so, and chastises anyone else who has repeatedly than one who admits she did and can explain why she considers it a mistake or regrets the decision. The latter is someone who is less likely to repeat a mistake with me because they know first hand the hurt, problems, and regret that comes with the mistake.
A healthy you and a healthy relationship will look like this: You aren't disgusted by the fact she cheated before because you know she admits the mistake and can tell you what she learned from it. You aren't disgusted with it because you know that you've given her no reason to cheat on you.
I would guess that this chick will never cheat on you. What she will do is dump you if you she feels like it isn't working out or she isn't really invested in the relationship. That's not a mistake, it's the right thing to do, and from what little you've told us, is what is likely to happen long before she cheats on you.