NEED ADVICE: I only really like having sex to be close to my partner, not for the “fun”

I feel weird. Everyone on this app and my friends go on about their sex lives and say it’s just fun and whatever. But when I have sex with my bf it’s because I want to be close with him and enjoy that time with him, I don’t like sharing our sex life because that’s an intimate thing that stays only between us. I have a low sex drive too and he has a high one. So sometimes we just have sex for a little bit and then neither of us finish bc I tell him it’s not important to me and he respects that I just want to do it for a little. This isn’t every time obviously, I know he has needs. But like because of that I have a problem with him masterbating to girls on Instagram (which includes reposts of tik toks). I feel like he’s pushing me aside and introducing random people into our sex life because his brain will associate those random hotter girls to that orgasmic feeling and therefore it’s not just our thing.

I have talked to him about it and he says looking at other girls doesn’t mean there’s anything wrong with me or I’m not attractive enough but I just cannot see it that way no matter what I do and I’m so hurt rn but I don’t want to bother him further about it.

I know I’m probably wrong for thinking like that and I know I’m probably weird for viewing sex how I do. I just need another perspective. So please if you see it differently than me then share your perspective on sex with your partner and WHY you’re ok with him using other girls to get off.

Also idk if it matter but we are both each other’s first and been together nearly 4 years now (both 21 years old)