S/O OBSESSED with threesomes UPDATE

First off, I’m completely straight. I have absolutely no desire to even make out with another woman. I’m very protective over my S/O and the thought of another girl giving him a blowjob/having sex with him makes me feel physically sick and angry.

We’ve been dating for almost 2 years now and it’s been the past 2 or so months that he really won’t drop it.

He wants me to download tinder and other swiping type apps. I’ve talked to girls and I even compromised by sexting another girl with him (just sending videos of us having sex while she got off). I thought that would satisfy him but I think it only made him desire this fantasy more.

He tells me he dreams vividly and regularly about another girl and I in the bedroom.

This obsession makes me feel so inadequate, and we’re both young so I feel like he’s bored of me and wants to have sex with other people???

Please help, I’ve talked to him like “all we do is talk about threesomes can we stop now?” Then he gets all mad and gives me a type of silent treatment and makes me feel guilty like “sorry for being annoying”.

I’m desperate for some advice.

Update

Just had a really big cry, and he walked in on me crying and was like “what’s wrong?” I simply said “I feel bad” and he must know how I’ve been feeling cause he said “please don’t tell me it’s about what I think it is” and I said “I’m sorry I can’t have a threesome. I don’t think I ever will and you can leave me if that’s disappointing”. We talked it out for a bit, then he said he’s really sorry he’s made me feel that way and promised to never bring it up again. I feel good about it at the moment, but we’ll see how long it keeps up. I’m happy that he knows how I feel. I’ve got home now and he’s texting me this.