I can't seem to get over my boyfriends ual past!?

I have been dating my boyfriend for 6 months now (although we talked for 3 months before we got together, so unofficially 9 months) when we first started talking i told him that i was going to wait until marriage to have , and he was totally fine with it! but in his other past relationships (he's had 3 girlfriends, one for 2 1/2 years,1 year, and the other for 3 months) he slept with all of them in the first few months of the relationship. people all over school have spread stuff about him being a addict, but he has never done anything ual towards me. I know its stupid to worry about things like this, but i can't help but every time i think about him with those girls i get so tore up and feel so down. and i feel like i have to compete with them (especially since they were all stick figures, and I'm more of a curvaceous girl) is there any advice to just help me stop being so insecure!?