Trouble accepting my boyfriend’s past

Hellloooo I just wanna know if this is like normal or how to fix the issue in my brain. So I’ve known my boyfriend for about almost 3 years but we’ve only been dating for about 1 year and he’s a few years older than me. I found that I tend to get my stomach twisted a lot or get insecure and compare myself to his exes. Particularly I find that a casual relationship he had with an older woman tends to bother me and I find myself comparing my body, face, and skills as far as sex to her a lot. I’m not sure if this is the cause of my insecurities or if it’s a combination with being just sensitive and easily jealous in a relationship, but around 2 years ago or so he used to talk about her in a group chat and how her body is amazing and how she’s good at sex and stuff even texting while she was doing stuff to him and thinking about it just makes me so sick and icky even though it didn’t bother me back then cause we didn’t know each other too well. Were very open about this kinda stuff and have had many talks about it and he always reassures me and tells me that I’m the best he’s ever had and how those relationships mean nothing to him but I sometimes feel as if he’s just trying to make me feel better. I trust him very deeply, I just get super insecure and hard on myself sometimes. Has anyone else had similar issues or can give insights on how I can ease my mind a bit? I really don’t want this to continue to be an issue just because my insecurities and self hatred won’t go away.

It should also be noted that I’ve had a lot of self esteem issues in general but especially when it comes to sex I tend to believe that all of my worth relies on being an object of sex, and I get anxious or insecure when I have to say no or if I don’t wanna do something or am uncomfortable. I think my ex did me dirty on that one. my belief is that my current bf’s ex wanted to have sex and had a higher sex drive more often when she was with him, and since that’s where I place my worth it makes me feel really insecure, especially in the fact that sex can someone’s bring me shame and anxiety when I don’t want to, or don’t feel comfortable with it.