He honestly sounds like a dick. There’s no point in bringing up so much detail about previous experiences unless you two WANT to have a friendly conversation about it.
It’s disrespectful to you because you’ve already asked him many times to stop. It’s not ok to disregard your partner’s feelings. It’s also disrespectful to all the other people he’s had a past with. Graphic details about happened in their sex lives stays between them, especially if it’s about their own bodies. His sex stories are not trophies and he has no right making comments about his previous partners.
If my partner kept talking about his past while knowing how much I don’t appreciate it and laugh in my face afterwards I’d be gone. That level of insensitivity and carelessness says a lot about who he is.
I don’t think the problem here is his sexual past. The issue here is that he’s dismissive, weird, and downright rude. It’s okay to talk about sex with friends and your partner but you’ve clearly told him to cut it off and he purposefully continues to make you feel bad. Your partner should never intentionally do anything to make you uncomfortable.