AITAH for wanting a monogamous relationship?

I (20M) was dating my partner (19F) ever since senior year of High school to now. We were doing fine until she got in contact with her exes one day and she pressured me to let her talk to them for closure. I obliged thinking nothing of it. I soon found out one of her exes she left to date the guy before me. She told me she never got to say goodbye. I felt bad and let her continue talking to him. Fast forward…. It’s been three years now and we’re starting to have a rough patch.We are living together. Communication was not there. I had just gotten fired last year and she was tired of supporting me. We meet at a Coffee shop and discuss what to do. She offers the idea of a Polyamorous relationship and expresses the desire to date someone else. I stand my ground expressing I only do monogamous and that my feelings would be hurt if I saw her with someone else. She proceeds to break up with me to pursue said person. I bring up with her how I feel hurt. To no one’s surprise the one she is dating is the ex she left because he was single and she still had feelings. I tried to bring up how I was hurt she moved on too fast and she said “she didn’t” and now I am conflicted. Am I the Asshole?