Proper way to issue an ultimatum?

[amg2]

(Cross posting)

I have a question about seeing other people. On D Day 9 weeks ago, H and I agreed not to. Shortly thereafter, I said I was willing to "look at possibility of staying M if he was in IC". Nine weeks later he is still not in IC and we have not established whether we are working on M or not. We visit a couple of times/week, though I have recently decided to go pretty dim and not see him during the week unless he spends weekend time w me as well.

I have been thinking (ONLY THINKING) about casually dating. Due to an incident I won't bother to explain here, I can tell that my H thinks the possibility of me dating is absurd, and that there's no chance I'm doing that, and if I were it would be a big secret.

I'm very close to (how close?) doing this if I want to regardless of what he thinks. Apparently he isn't realistic about this.

What obligations do I have to make him aware of 1) what I'm
thinking now and/or 2)IF I decide to date?

THANKS