@duck128,
Our opinions really don't matter.
Ask her. In a NON-accusatory manner. As in, during that time when you spent a few nights at ___'s house, did anything happen?
Be prepared for an answer that you might not like. But if you really, absolutely,
oh my God I will never sleep well again until I find out want to know, then have at it.
Or maybe wonder forever and don't ask.
Or maybe split the difference and get some counseling. And try to get her to come along with you.