Be really freaking romantic. If she is still unreceptive, talk it out again, and tell her that you need her to be honest and open with you about it. That you want to know if something is wrong (definitely do not accuse her of being with another guy though). Tell her that you are upset about it and just want to figure this out, because if this goes on, the hole in your relationship will deepen and that's no good. Be sensitive though. Perhaps she is having a problem or is having pain during sex and doesn't enjoy it because of that. Try to ask her if she is experiencing problems and be there to help her in whatever she needs. Just let her know that you are there to support her if something is wrong.
