Ok, haven't checked up on this thread in 2 days, but I guess you guys need more faqs:
1) She told me she was a virgin, so yes, she did lie to me.
2) I have always had this gut feeling that she was lying about her virginity. I don't know why, I just did.
3) Yes, the letter was kept inside a metal box with a keyhole. I found the key and opened it, and inside was a letter proclaiming their intimacy or whatever, and how close he felt towards her. I admit that looking in her stuff was wrong, but I just had this mistrust feeling I couldn't resist.
4) I would not have had a problem if she wasn't a virgin if she would have told me from the very beginning. It sucks balls that the one you love has hid this from you for a while.
I'm guessing she regrets having sex with the guy and he only used her for sex, which is why she doesn't want to have sex with me; maybe she's scared that I'm going to leave her. I honestly still don't know what to do, or how to present this new found information to her. She's going to be furious that I looked in that stupid box, but I guess I have to man up and face her....