I am SO not an expert in dating, it's not funny. I have not been on a date in many years, and I don't plan to ever date again.
I'd rather set my hair on fire and then try to douse it with gasoline.
So you can take everything I say with a big grain of salt.
HOWEVER....
I know this much. Giving someone an ultimatum is usually not a good idea when you are dating. I have heard this countless times from my female friends:
"So I told HIM, we've been dating for over a YEAR and I need some kind of proof that he is committed. I want to get married before my uterus dries up and falls OUT!"
"You tell him you want a RING, girlfriend! He needs to know he is NOT the only fish in the SEA!"
and on and on and on - let's all drink margaritas and dance around singing Beyonce's "Put A Ring On It."
Then the Complainer decides she will just lay it on the line with the Guy.
Now in Hollyweird, it plays out like this. Complainer lets him know she needs him to commit to co-habitation or marriage. He balks. They break up. He dates other people and then realizes she is THE ONE. He goes back to the Complainer. They go off into the sunset.
Does that happen in real life? Probably not so much.
My parents got together because Mom gave Dad an ultimatum when they were dating. She had advanced to the scary age of 22 and was without a husband. In 1957 that was getting into Old Maid territory. Mom's aunt Miriam had her whole prayer circle trying to get her hooked up with a husband.
Mom said to Dad, "Look here, I'm not getting any younger and I want to get married and start a family. If you're not going to marry me, we're through."
However, most of the time ultimatums don't work. Nobody likes them. They are not conducive to happy feelings.
If you are seriously pondering whipping out a nasty old ultimatum, re-think. Sometimes you can finagle the result you want if you choose your words carefully. For instance - "I understand your feelings and I respect them, but I have to be by myself for a while, to reflect on how I need to move forward" - is less harsh than "put up or shut up."
Once you've said those diplomatic words and walked away, you are depriving the other person of your company - and you may choose to even [gasp] stop texting, emailing and/or calling. That does the same thing as a Breakup Ultimatum. However, you are saying I have to figure out how to take care of ME. You are not indicating the other person HAS to follow YOUR program.
If the other person is deprived of your company for a while, one of two things will occur. They will decide they desperately need you back and comply with your wishes, OR they will decide they actually DON'T need you back in order to be happy.
Either way, you've not made an enemy.
Ultimatums, however, make enemies. They set you at odds with the other person.
If you really want the relationship to thrive, you have to let it be a natural occurrence, not a forced thing. Creatures forced into traps will almost always try to get OUT. That's not conducive to a long and happy situation.
So beware the Breakup Ultimatum. Understand the risks, and ponder better ways to accomplish your goal.