Okay SS, I know the "money" is not the issue, but it is if he cannot be reliable. What happens when there comes a week you need it and he doesn't have it, or doesn't pay it because you have let it go before? Your kids are still in the middle then. He tried to pull the "Now I can't have the kids, you have all the money" but backtracked and now has money for the kids and a tree etc.
He is testing where you are setting your boundaries and what you are willing to accept. I think you have to decide what is okay and what is not and stick to it period. If it is pay each week, then it is pay each week. If it is more flexible, then maybe you need to define it better.
I am glad you are working on your tone of voice and try not to engage him when his behaviour escalates on phone or text. If he say "I can;t have children next week" again, (or something similar) just say, "I'm sorry to hear that" or something equally noncommittal.
I don't know if you have mediators or not, but that is always a good start as well.
I know what it is like, missing him more when you see him. ((()))
