I cannot stop ruminating.

Okay. My boyfriend(20M) and I (19F) have the same argument almost every week, where I come to him very upset, because something “triggered” me and I can’t stop thinking about every single woman that he’s been with before me or sent a dm on Instagram or talked to on a dating app. It especially hits hard because I knew his ex (and him) while they were together and they had a horrible relationship where he eventually cheated on her. He’s very serious about me in a different way, I just met his whole family and they were great, so I believe him that he won’t cheat but I cannot stop obsessing and ruminating over the fact that he has had so much more both dating and sexual experience than me. On top of that, a few weeks after we first started talking, hanging out, and texting, I already had (small) feelings but he had sex with some girl from a dating app twice. Which I just found out about recently. I hate that so much. I cannot stop thinking about it. Why did he feel the need to do that? It fills me with genuine rage. I know I’m being insecure but I literally cannot stop thinking about these things all the time. It’s driving me to convince myself that if I go out and have sex with someone else maybe I’ll feel “even” and I’ll realize that what we have is indeed special. Obviously I’d never cheat so I’d have to break up with him to do this but that just seems ridiculous. I don’t want to break up, we are great partners, and a good match, I could even see him being “the one”. Whenever I think about this large web of sexual encounters he has indoctrinated me into I actually feel my chest tighten and the very strong urge to run away as fast as possible. I am very protective over my body because of things that have happened to me in the past and I start to feel very upset when I remember that no matter what I do I can’t take that back, no matter how hard I scrub in the shower, my soul is embedded into this ever expanding web of people linked by sex and he’s to blame for being with so many women prior. I hate it so much it makes me nauseous. How in the world do I make this terrible pain end? Am I just looking for a reason to self sabotage? Or is this genuinely a good reason to be upset and confused? I’ve tried to choose peace in the last few days but sometimes it feels absolutely impossible. I’d appreciate any input, thank you.