How to deal with situation?

Cliffy, think of the consequences of not believing her compared to believing her! If you believe her and find that it's a lie and she just had a fling with a rough individual, then you are going to be extremely upset with her. If you don't believe her and you find she "was" d you are going to be extremely upset with yourself. I would approach this with compion, not intellect. If you are wrong big deal. The truth will not change your next reaction. Just postpone it for awhile.