You know, this needs to be nipped in the bud NOW In order for the wedding to continue. This puts you in a very tough place that you did not cause or create. Has she done anything like this before? Sounds like she does not share your values when it comes to fidelity and the guy has no respect for your relationship. "I don't know" is a careless, thoughtless and cruel response knowing you 2 are about to marry. And her projecting her wrong doings on to you is backwards. It cuts off the possibility of continuing the dialog in order to fix the problem. I know marriage vows to one another are the core of a marriage working out. Maybe you 2 can go over them before the ceremony to make sure you are on the same page. with the information you have shared, this is the only solution I have to offer you. Keep posting. We really do want to help.