This is a tricky one... on one hand, you've only been together for 3 months, so if you are going to bow out, you should hurry up and do it before you both invest more time, emotions, and energy into what you have going. Was this conversation brought about randomly? Were you just talking about the past, or did she bring it up in a boastful way? I ask because you said you don't judge people for their past, but here you are, judging your girlfriend for her past. She didn't have to disclose any of that information to you, but she did because she wanted to be closer to you. Unless, of course, she brought all of this up in a boastful way, and you also see other signs that she isn't being truthful to you within your own relationship... that's a separate issue though. Also, it's worth noting that she wasn't the one in a relationship at the time she hooked up with those guys - they were. Why is the mistress always looked at to be worse than the person who is actually in a relationship? When adults want to get down, they will get down, regardless of their circumstance. However, just because she hooked up with guys who had girlfriends or wives, doesn't necessarily mean she would hook up with someone else while she is dating you. I think she may be acting jealous and assuming you will stray because she has been with guys who were in relationships, so she sees how easy it is for some men to cheat on their spouses. I think if this information is too much for you, and if you can't look at it objectively, then maybe you should cut ties with her. You can find another person who doesn't have the same exact past as she does, but everyone does have a past behind them. It doesn't make them who they are; who they are depends upon who that person chooses to be at the present moment.
"Caring is not an advantage."