Me (m) and my girlfriend have been together for a little over a year now, but a month or 2 ago she tried cheating on me with my friend but he told me. We talked about it and everything and she hasn't done or tried anything since, but I did something bad. I've been staying with him and I fell asleep with him last night and he rubbed my back but started going lower and eventually it got to the point where he was grinding on me and in the moment I really liked it and then he asked me if I wanted to go further and I told him no because I have a girlfriend and it felt so wrong, so he agreed, I went back to my room and cried because I genuinely feel so shit about what I did. I called my girlfriend and I wanted to tell her what happened but I didn't because where I am is:
Do I tell her and release my guilt and let her decide what happens next or
Do I spare her from being heartbroken because of what I did and just never talk about it again
(Throwaway cus she knows I have reddit.)