My gf told me to stop having sex for a couple of weeks so I was ok with that. Last night, I was going to her house and when I ringed the bell nobody answered the door but I knew she was there because I saw the lights on in her room, so I walked to the window and I looked through it and I saw her totally naked with her neighbor doing her. More than pissed I felt sorta sick. I mean I thought she loved me. I don't really know the guy but if I find him on the street I going to beat the hell outta him. I haven't talked to my gf ever since and she tried calling me and she even went to my house but I didn't answered the door, so I guess she already noticed I acting "weird" I don't know what to do. I still love her but I don't think I could forgive her.