Ditto what RocketRiver said. Don't ask a question for which you wouldn't like the answer. If you can't control your mind, you are out. Treat people with respect, if they honor it, all is well. If they don't, move on -- it's their loss anyway.
dont worry about it. It's a bad account and very vague. Plus, face the facts...your pee pee isnt the first one she's had.
it shouldn't matter how many guys she has been with before you came along. what matters is that she cares about you and that she treats you well.
all the important questions you need to ask yourself ... how important is past chastity is to you? so she possibly had a one night stand, so what? can she faithful in the future? which is more important, she had a one night stand or your cousin knows about it? ... there's more but thats a good starting point.
