Hey, Sadie. I've been dealing with a situation, not similar really, but relevant maybe. I've been trying to get a guy to leave me alone. Simplified version: One date, texting often and suddenly he believed we were in a serious, exclusive relationship. I asked him to back off. He kept texting. I told him that wasn't backing off and asked him to stop texting and go away. He kept texting.
The scenario devolved to me ignoring his texts until he'd say something similar to your ABF's message, or something that made me mad, or proposed marriage. At which time I'd respond. Each time I'd tell him I wasn't going to talk with him anymore. Ignore, respond to plea for closure, said good-bye, said no more contact. Ignore, respond: tried to correct an accusatory statement, told him no more, leave me alone. Ignore....
Seeing a pattern? I admit it took me a while to. He'd keep trying until he found a button I'd respond to, and I'd break my 'I'm not talking to you anymore'.
So, I've told him to leave me alone. I've said I do not want to talk to him. I've said good-bye. It's been a couple weeks. I've stopped responding and the text messages have slowed down.
A line from a favorite movie: "I've spoken my piece and counted to three." There's nothing left for me to say to him. If I respond, not only do I break my boundary, it resets his TU _wants_ to talk to me belief. (And confirms that TU is some one who can be pestered into doing what he wants.)
You've told him no contact until he's serious in recovery. You do not have to give him any further closure than has already been given.