Hey guys, help me out here. (Sorry for english mistakes)

Me (22) and my girlfriend (24) ended up sometime because of religion. So we worked it out and tried again. But she was not invited to my sister's wedding (it was like 6 months later), so on the weeding day she and her mother went to a nearby town and slept in the house of friends, they have one 22 years old soon. But her mother left with some commitment and she stayed the weekend. They left for a dance with a group of friends, she said nothing happened. But I can not stop thinking about it, and I do not think she would ever admit it.

And writing this just make me feel even more pathetic...

Should i just leave her? How can i make her confess? She has never done anything like it, but i don't know, AWALT, right...? Or should i give her a chance and work on myself to let this go? She is a good girlfriend we we're both virgins when we started.

Edit: I don't know if this should count but we have a planned trip for Europe 12/12/2017.