Uhm excuse me WHAT

I'm skipping everything to just get straight to the point. I've been with a guy for almost a year but recently he won't stop asking for a threesome. No, I'm not up for it. I don't want a threesome. He says I have too much emotion and feelings about it but he's my man? I don't want another girl touching him in ways only I should be. He brought it up again and i said let's get a guy involved too so I'll have someone and he immediately shot it down saying it was gay. He has threatened to break up with me for not wanting a threesome. What do I do? Are you guys okay with threesomes?