Here's another distinction -- about "ultimatums" vs. "boundaries" -- that may help you summon the courage, FVF:
The best way I can answer that is that if you make it about HIM, they will come across as "demands" and being "controlling."
If you make them about YOU, and what YOU need, then they are "boundaries of personal integrity."
Example:
"I forbid you to see OW" = CONTROLLING
"I can't live in an open marriage" = BOUNDARY
"You need to check in with me every day, and give me your cellphone bill!" = CONTROLLING
"In order to feel safe in our reconciliation, considering your recent affair, I need to know that you're no longer talking or texting her by having the cellphone bill come to me for awhile" = BOUNDARY
"You can't talk to me that way!" = CONTROLLING
"I like ME too much to allow myself to be spoken to so disrespectfully. Please come back when you've calmed down, and we can talk further." = BOUNDARY
Make sense?
It's also HOW you say it. It should come across as something you HATE to have to even ASK for, and that you'll COMPLETELY UNDERSTAND if he doesn't feel he can do it, but hey -- this is what I need right now. Let me know."
Puppy
P.S. Look up pearharbor's old posts, for a great example of a woman successfully (and strongly) positioning this to her partner.
