Boyfriend asked about 3somes and I'm confused?

My boyfriend and I have amazing sex and we like trying new things.

Recently, He asked me about trying a threesome and thinks both MMF or FFM would be hot. He thinks it'd be so hot to see me going down on another guy while he's doing me from behind but he doesn't wanna do anything with the guy.

I told him I've never thought of being with another guy except him and I don't think I'd like the idea of sharing him with another woman. I told him I haven't thought of 3somes before and would have to really think this through before I commit to trying it. And then he said, it's a fantasy he's had and if it were to happen, he wants it to be with me and not another girl.

I don't get what he means by that because doesn't a 3some (if FFM) involve another girl as well? And how would MMF work if he doesn't wanna do anything with the guy (not that I'd want him to either but just confused)? He's also not into one night stands or casual flings so I don't understand why he's asking for a 3some?

We've since dropped that subject since he sensed that I'm not comfortable with it but at the same time, I'm afraid I might be holding him back from what he wants, although this doesn't mean I'll force myself to do something I'm not comfortable doing.

Any thoughts on this would be welcomed!
Boyfriend asked about 3somes and I'm confused?
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