The other thing about ultimatums that I've finally gotten is that you are taking on the responsibility for someone else to change, and I frankly, don't want that responsibility. So, you give an ultimatum, they comply and change, but that means you are holding the keys to the future--he might be mad that he's missing out on what he REALLY wants to do. You might find it didn't give you the happiness you wanted.
If you simply set a boundary and act on it, that's more of an "in the moment" thing. It means, "I'm not holding you accountable in the future." It's easier to detach from the results.
I say this, because my little winter place is waiting for me at the end of the month. I REALLY don't want this to be, "I'll be back IF you change." I just want it to be, "This is what I'm doing now because I can no longer tolerate my life as it is. You can do as you please."