I don’t know what to say

Ever since we’ve been dating, my husband has these times where he’s can’t stop think about me with my ex’s or or ex-sex-partners. It’s like he overthinks about it all and sometimes hell be like “idk why but I can’t stop thinking about you with your ex’s or you and the people you’ve had sexual with.” And I know people can get jealous and overthink and make them insecure but he KNOWS I’m not with them anymore. He KNOWS why those people and I don’t speak anymore. He KNOWS I’m better off without any of them. And he KNOWS I don’t want anything to do with any of them, but yet he still thinks about them and he overthinks about it to the point where he gets jealous and mad and fights about it with me. I try to always reassure him that he’s the only one for me and that I’m his and his only, but it’s like it’s never good enough and he’s always like “sure I am,” or “I wish you were never with them,” or “I wish you never slept with them.” Like I understand it makes him upset, but it seems like he just overthinks it all just to have a reason to be mad at me. He’s cheated on me, but I’ve never cheated on him—ever. And he always brings up “well it hard to believe that you only want me, especially because you can’t even remember who all you’ve slept with” (which I have a terrible memory, but I’ve told him all the people I’ve slept with after I wrote it down - which there were only 4 others, for all you slut shamers). And like I always try and make him feel better and try to get his mind off of it all but it just seems like he always tries to make me feel bad about all of it and it seems like he always tries to put me down because of it and always throws my past back up in my face. It’s the past for a reason. It’s done. It’s over. He is my now, and he is my future. I don’t know if it’s because he’s insecure or what, but I just don’t know what to say to him anymore. Anything I say is never good enough. I don’t know what to do anymore. Does anyone have any advice on what I should say to him to make him feel better?

(Also, I’d like to add that I am his first serious relationship and the first person he’s ever had sex with-so maybe all of it is from insecurity? or jealousy? because I’ve been with other people & he hasn’t?)

EDIT: I’d also like to add that whenever he brings it up and I try talking like an adult about it all, he always starts a fight and says that he hates me saying (when I just ask) that he/is he jealous because “he’s not jealous” and it “pisses him off when people say he’s jealous because he’s not”