Ultimatum from boyfriend?

So tell him that. If he apologizes for dealing with it this way and is actually willing to talk the situation out, maybe there's hope. If he still thinks that holding his feelings inside until he's willing to end the relationship over it is a better course of action than openly communicating with you when something bothers him, then tell him to take a hike regardless of whatever you decide to do about the thing he objects to. It's just not going to work out long-term.