Jealousy is driving me crazy

I’m actually going crazy because I don’t know if it’s just me being too jealous or if everyone goes through this.

I’ve been with my current boyfriend for almost two years now. He’s my first love (I’ve had relationships before him, but nothing meaningful) and also the first - and only - guy I’ve ever had sex with. The problem is, I’m not. He’s had more relationships than me and also wasn’t a virgin when we got together, which is absolutely fine. But I’ve always found quite disturbing the thought of him having sex with other girls. He’s had sex with three (from what I know) girls before me, and he wasn’t in a serious relationship with any of them: the first one was a girl he went out with for a couple of months (who then dumped him), the second one an American exchange girl who was staying at his friend’s house and the third one he slept with just before he met me, and they just went out for a little bit. (He actually says he ended things with her the night he met me)

I know I shouldn’t care, but we’ve had some problems in the last few months (everything started when I found out he kissed a friend of his while he was drunk, but this is not the problem — and if you want to comment just to tell me to break up with him because he cheated, please don’t) and now I’m even more jealous than before. I keep thinking about this and I’ve went through his Instagram a billion times just to see him interacting with girls from his past (obviously before he started dating me) and it always hurts me so I know I shouldn’t be doing this.

I casually brought it up with him, saying that he doesn’t have to “worry” because I’ve only ever been with me, and he dismissed me quite easily which, again, hurt me a bit.

How can I stop thinking about this?

P.s. I’m not the classic “jealous type” who doesn’t let him hang out with his girl friends or talk with girls at all, I do trust him about this. It’s all that happened before him that is driving me crazy, which makes zero sense