Bf's fantasy making me uncomfortable

I actually thought we've been having better than usual sex lately. But the past few times, he keeps bringing up this fantasy of his that weirds me out because it not only involves strangers, but also because he's the kinda guy that gets irritated when guys would hit on me in front of him, so I was shocked when one day he suggested I maybe give someone a BJ while he does me from behind. And then he's even asked if I'd give him a BJ while this complete stranger is inside me! I'm so mortified, I never want to make him feel bad or like I'm judging him but I'm honestly so weirded out by this. And a bit hurt for some reason. At first I thought he was wanting to work up to a FFM so I told him there would never be another girl in our bedroom unless he was ready for me to leave him. But he's not that interested in that, he just wants to see another man have sex with me.

He's not forcing me to but is asking I consider it. I said would consider, but know I don't think I ever will. I'm trying to have an open mind but idk how to deal with this. I love him but can't/won't sleep with other men for him. And I can't figure out how he got this idea in his head!