Hope ~ Sorry to hear about the latest development.
You can't control what he decides to do, like others have pointed out.
It sounds like you are seeing this in black-or-white. Either you get your way (12 months), or he gets his way (6 months). Perhaps you can say:
"I strongly believe 12 months is more appropriate for reasons XYZ. I also understand you think 6 months is adequate. I respect we have differences, and respect that you are considering D4's emotional well-being in making your decision."
Then you've asserted your opinion, you've released control, and you've nodded to the fact your H is considering D4 (rather than parading women within the 1st week as many people do).
In my situation, I believe my kids are being introduced to a BF without any discussion with me. Some people have it even worse than that.
Everything we learn in DB applies to co-parenting as well.
