SBJ ... its tough man ... especially with the Holidays.
I have here on sale a case of Cherry flavored STFU smoothies ... buy some. You were gold till as you admitted you got pulled in and said to much.
There are 2 schools on "Friends" some will say the FZ is better than the A-hole Husband zone ..... others like myself feel its important to make it clear to them we will co-parent to the best of our abilities but in no way are we interested in the demotion from husband to friend. I am guessing you fall into this camp as I did.
I know much of my advice come with a story .. this is no different. I was in the military and went through SERE training. For those who do not know what this is .... its Survival, Evasion, Resistance, Escape. I never had to use it ... till .. yup .. MLC. Was not shot down and landed behind enemy lines it was with my MLCr. So in a sense when you feel this coming on (over time you will notice it before it happens .. in some cases you know before you even see her that its coming) you have to adapt to this mind set of only giving them Name, Rank and serial number ... but in this case I memorized the following concerning D and what the MLCr has fantasized it will look like, because this is in fact what you are battling ... in her head you will be the best of buddies and she can chase that euphoric pipe dream.
"I do not agree with your decision, but I respect it and will not stop you from what you are doing, that is your choice. However I am not interested in any friendship (cake-eating), I will co-parent with you to raise our wonderful children to the best of my ability."
End of conversation and you bounce off to do that thing you have going on. Deliver it in a kind matter of fact way and off you go. Brace for the backlash as it will come ... but I believe they must realize reality will be much much different than what they dreamed up (understand this has been planned for a bit ... and they have it all laid out in that fogged up noggin of theirs)