Advice?

Hey everyone! Just looking for some advice here. I was with my ex for 8 years but we’ve always broken up many times because he’d leave me for other girls, cheat, etc… every time we’ve broken up he’d immediately get with other girls, post them, sleep with them, do things with them that we used to do. Even though I’ve been through that pain of always seeing him with other girls, I always feel jealous every time. Idk if it has to do with the fact that he was my first boyfriend, the first person I lost my virginity to and was my first everything. I just want to stop feeling this way because it’s stupid… but I don’t know how. I hate feeling jealous because I know he’s not a good person and uses girls like toys, it’s just I always end up feeling jealous…