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I don't think the boyfriend is nuts, although he probably feels that way right around now. Threesomes are, by a lot of folks' standards, pretty weird. And as long as those standards are applied across the board (you, me, men, women), they are not double standards.
Now maybe it would be really nice if the BF were relaxed about this. But clearly, he isn't. Also, if it bothers him this much it probably touches a nerve that isn't going to get soothed by six months of therapy.
So, yes-- call things off and look elsewhere. Do what you need to do.
But don't knock this guy for thinking that weird stuff is weird.