Been following your story for a while and impressed with your courage.
I think it is time to face that he is not going to be the poster child for great parenting. I know your heart aches for your young children, but I do think it is a blessing to be younger. None of us have recollections of being three. As she ages, the life she sees will be the life she knows.
You can't force someone to parent. Mine was a somewhat involved and supportive dad and now has not seen one child in a year and has seen the other twice very briefly. My guess is that yours will also see them less and less as he gets pulled into his shiny new life, and then maybe after a time, not at all until he works through his issues. After two years, mine does seem to be making a microscopic effort to up his game with the kids.
He wanted to push this. He wanted to force you into this. Don't keep helping him out. Don't push him to take the kids when he is supposed to. If he doesn't, more time for you. Be the stable parent for the kids. Having one makes all the difference.
If you start making concessions on the timing this early when he hasn't planned in advance for a change, you will spend the next 18 years chasing him to see the kids and letting him pop in whenever he wants. Trust me, that is hard on the kids. Mine are older and they say they would rather see him regularly or not at all. They hate that they see him only when it is convenient for him.
Hold firm to your agreement. Don't ask him to be a parent. Let him find his own level.
You won't nice him back. He won't respect you for being pliable, he will just take advantage of you until you don't allow it anymore and then he will build you up as the bad guy anyway.
More detachment. More letting go. Less communication. Let him tell you in advance when he needs a change and if it works for you, say yes only because it worked for you.
We all ache for our kids, but a three year old is going to get over this quickly.
