should I be upset?

Me & my boyfriend have been together for about 2 years! Throughout the relationship we would break up over small petty things but the most recent breakups he went and kissed 2 different females while we weren't together. I know it wasnt cheating but we are back together now and I can't get it out my head😩. What should I do, I already expressed how I felt to him about it but it's still ponders in my mind. It just hurts knowing he would do something like that