My girlfriend meets her girlfriends every friday night. They go for a foot massage, or shopping, or drinking after work on every friday. This friday my one friend called to tell me that he saw me and my girlfriend go into the movie cinema and that he had called out to me but I didnt hear.

I cut on him and called my girlfriend and she said she is in a movie. I cant help think that she went for the movie with some other boy. Casually when i asked her how the movie was, she said it was ok and quickly changed the subject. But normally, she talks a lot about the movie she saw and what her friends said and did, etc.

Should I ask her directly that my friend saw her with another boy and assumed it was me and called me? How can i know if my girlfriend is cheating on me?