Advice please 😫

Need some non biased advice, me and my boyfriend of 3 years split up for about two months, we thought it was over for good so we both talked to other people and tried to move on, we worked things out and are back together now, BUT I can’t get over the fact that he liked another girl while we were broken up. I’m literally obsessed with thoughts, is she prettier than me, what was she like, was her personality better than mine etc. it’s basically eating me alive, I’ve told him about these feeling and he re assures me but the feeling comes back a few days later and I know if I keep bringing it up he’ll eventually get annoyed and it will cause more problems. I want to feel normal I want to stop thinking about her and just be able to move on. I don’t know how. I don’t want this to bring down my relationship.