Y'all have a terrific counselor-- and you covered all this ground in an hour? Fantastic.
I, too, struggle with my bf imagining his mom's and his ex's words coming out of my mouth when I have never said those things. I'll say something in a very mild tone of voice and he'll think he's repeating what I said back to me, but it will be in a very sarcastic, flouncy, ultimatum-ish kind of way. I guess he really does hear it that way. For instance, I learned a while back that the phrase "why don't you" followed by any request for action, no matter how benign or innocuous, is a major, flame-throwing, nuclear-tipped hot button. When he hears the phrase "why don't you," he shoots first and asks questions later. That has eased since he's been going to the C, however I still wince when I accidentally use it... I'm like Pavlov's dogs-- very easily trained.
Your H's reaction to "I can't live like this indefinitely" reminds me of Mrs. Hairdog's position that she has to KNOW that Hairy unconditionally accepts her perennial "no" in order for her to EVER consider saying yes. A real Catch-22.