So what? Every man wants his girl to tell him he's the best in bed. We all want a girl who's never been touched before us. We somehow think that just because a woman has had guys before that she'll have guys after us. You know what? In most cases it's the truth. She might be the girl you end up with for the rest or your life or not. Who knows? All i know is, is if you let her sexual past interfere with all the good she's willingly giving you now you're doomed.
She told you because you asked, not because of some moral obligation to confess her sins to you. She told you in confidence because she felt you were secure enough to shrug it off. If you let her past bug you that much you're doomed to ruin the relationship. She's with you for a reason. Don't forget that.
I'm currently with a girl who's had a pretty wild past - Even up to the week we became exclusive. It doesn't bug me in the least. Honest to god. My first relationship the girl didn't do half the things my current girl did. It was her choice and her right to do it. I said sh!t to my ex that would make any loyal girl with an insane attraction to a guy run out like her goddamn house is on fire. Things like "god i don't know if i can get over it" and "I can't believe you did that. I don't know if it's going to work, we're just too different"
I'd have her in tears at the end of the convo begging me not to break up with her. Eventually it got to the point where me judging her got stale and she just didn't feel like dealing with the jealousy anymore, among other things. (not saying she didn't have her fu<k ups too. My insecurity was a big factor in it not working out though)
Point is she likes you and wants to be with you. Don't ignore that fact. Every girl has done something morally questionable at some point or another. It was the right time and place. I could understand your problem if she was married or had a boyfriend and had no shame or remorse in cheating, but that wasn't the case, was it?
Edit: You should read Squirrels' latest post on how dark seduction can get. As I said before the conditions were set up for her to be gangbanged and she liked it. Did she like it enough to do it again? Is she a serial cheater or swinger? We're all sexual creatures and sometimes, based on a girl's sexual appetites and moral hangups, things like that happen. It's been happening since the dawn of time...or dawn or man...or something.
I'd see red flags if she said she cheated on her exes, lied to her exes, or withheld any important information with them. I'd see redflags if she flaked out on you and gave you excuses to NOT have sex with you. What other redflags to you see?