I don't know what to do or who to talk to.

I consider myself to have lower sex drive/interest to the point I consider myself some form of asexual. I was open about this with my boyfriend before we got together. He has a higher sex drive & "requires" an open relationship on his side to mess around because otherwise he feels he'd be likely to cheat at somepoint. Due to past experiences I agreed to give it a try thinking it would take some of the pressure off of me. It has not. Especially since having our son 21 months ago I have like zero interest but still give him sex & bjs to keep him happy. Which i feel like & have told him is making me resent him. Despite our arrangement he says he requires sex in a relationship & won't be in a sexless relationship. Often leaving me wondering if we're even together still. I would like to just hangout & enjoy his presence/time together but just dread it now as he expects & feels entitled to sex. Sorry this is kinda all over the place but when our son was a week old he snuck out drunk & ended up having sex with some random. Which to me was a huge slap in the face as I had just had our baby. He says he didn't think it was a big deal or that the timing wouldn't matter. Sorry it does & hurt me so much. But I'm still struggling to get over it as to me it makes me feel like he doesn't care about me/prioritizes his wants over everything else. Like he's straight up like I'm still going to see other people.