My ex broke up with me after saying he was willing to try.

My ex and I were together for 2.5 years. The first year we were together he was talking to his ex behind my back. I found out and it was devastating yet he promised to never do it again and work on our relationship. A year goes by and no effort has been made on his part to help our relationship. No dates, no open conversations about the incident, no self improvement to help himself. Yet I was made out to be the bad guy in the end. I was told I was weaponizing what happened but I wasn't. I would have moments I'd get triggered and would vocalize why. What really caught me off gaurd though was him breaking up with me after sending me all these messages about how he wanted to work on things. Afterward he acted totally ok as I was devastated and heartbroken. I don't understand how someone can just give up on somebody like that. All I ever wanted was a healthy connection with him and he treated me like a problem.