Did she cheat on me or am I overreacting?

Anonymous
For a few months now my ex and I have been seeing each other and going out on dates every once in a while. I’m the one trying to convince her to forgive me and get back together with me. She has made it very clear that we’ll never be in a relationship again but we still have casual sex from time to time. I was staying in her apartment for a few days, she decided to go out partying with some friends and I got very worried, I called her a bunch of times, she got upset by this and told me to stop calling her, assured me that she was by herself and nothing would happen with another guy. She told me that but an hour later changed her mind and ended up kissing a guy she met. She came home and even though she denied it at first, she confessed everything and asked me to leave. I reacted very badly and got violent with her. I felt betrayed and cheated but now I feel like maybe I overreacted a bit. Did she cheat on me, is that possible?
Did she cheat on me or am I overreacting?
2 Opinion