I'm glad you were able to have those talks with him. Yes, I too would expect that a metamour isn't told "because she said so and wants it that way" but "we are" or "our agreement is" Be it for safe sex rules or scheduling or whatever decisions are made that affect other relationships.
I suppose if my husband said "I would like to do that, but Anne isn't comfortable with that now so it is off the table" I'd be fine with that, as it makes it clear how he feels and what he wants, but isn't worded in a way that makes me feel I'm being blamed. That however I'm more comfortable with in cases where I do expect to change my mind at some point, so the other parties know it's not a blanket this aint a possiblility forever. I don't mind metamours knowing I'm human, I'm allowed to have doubts or feel insecure or not like something.
I really cringe at that stuff because it's like the stereotypical complaining husband who is always saying "My wife wont let me". I didn't think that really happened but my husband's work appears to be full of guys going around saying that. The last thing I want is that same attitude presented to people my partners are dating .
Obviously everybody is somewhat different about what they prefer, so it's always good to go over wants and expectations about how to handle situations like that. I'm glad you were able to express what you wanted to him about your own relationship, and hope that it goes smoothly for you with the dynamic change.
Happiness will never come to those who fail to appreciate what they already have.