OK, so based on the other top comments in the thread imay be in for a absolute walloping in terms of downvote, but it might be healthy to read a contrarian opinion.
If it gets too badly downvoted I'll just delete it,but hopefully you'll have read it first.
I think think what he did was OK. It wasn't cheating, it wasn't devious. In his point of view, he may have thought the idea of a threesome was so appealing that the idea of you being revolted at the thought was unfathomable to him.
Wanting a threesome isn't wanting to cheat, it's wanting specifically to share something with you. From his point of view its something that you could enjoy too. This is clearly false, that's fine, I'm not trying to tell you to have the threesome.
The act of "setting one up" could have been just trying to make it so it's not awkward for you. (A miserable failure of trying not to make it awkward)
I'd also go so far as to say shame on the people who have supported your gut reaction of break-up without any further relationship context. With that said, I also wouldn't rule out a breakup, I just wouldn't storm off and do it while furious.
So, as far as advice goes, I'd say step one is to think about your relationship with this guy outside of this one incident. Does anything else in the pattern scream stuff like "jerk, manipulator, cheater, liar"? if yes, break up now
If no, and if outside of this one thing its time to think about whether this one thing is an actual deal breaker for you or for him. That means adult conversation time. How does he feel about you never ever ever wanting a threesome? If he's sorry he pissed you off, maybe there's room for working on forgiveness strategies.
I'd say that's up to you and would honestly be on your side either way... My opinion is that you're unlikely to find a guy that doesn't want to have a threesome... You're also unlikely to find one who isn't occasionally a well-meaning yet totally misguided fucking idiot sometimes... But you really have to consider who he is outside of this one idiot move before you break up. Is he a good, caring, loving guy? How do you feel about him otherwise?