My girlfriend and I have been in and out of our relationship for a while now and we've both confessed that we still have feelings for each other. While currently we're not officially in a relationship any more, we still talk a lot and she has told me she still loves me and that when I come to visit her home town in a month that she wants to get back together. I too have strong feelings for her currently and thought this was a good idea. (I should mention now that ever since I moved away to go to university we've attempted this 'long distance' relationship idea and while it hasn't exactly held up, neither of us have moved on from one another and therefore haven't seen anyone else). However, last night when I texted her and asked how her day was etc, she said that she's spending the night with a "friend"and I thought nothing of it. Then I saw her snapchat story and realised it was a guy and that he had spent the night with her. As far as I'm aware (based on no evidence what so ever but just out of blatant observation) they had sex. I mean who the fuck invites another guy over for the night and just "watches movies and hangs out".

I'm not sure what to do. I feel like although I don't know for sure what happened, I can be fairly certain. Should I just delete her off all social media and never talk to her again? Or ask her? Or just wait and see what she says (where I won't say anything to her unless she says something to me and then Ill bring it up OR act like nothing happened). Any advice is welcome, thank you.

EDIT: Yes I'm aware we aren't in a relationship so she isn't ''cheating'' on anyone (I should have rephrased). Thanks for all the responses so far, helps a lot. My question was probably more leaning towards ''should I talk to her and see what happened or just forget about it and move on'' and it appears the best answer is the latter.