Pax - wow, so sorry to hear you are still in the thick of it all.
Some people (and I expect your ex is one) just enjoy fighting for the sake of having confrontation in their lives. Playing armchair psychologist, I suspect he is just not the type who is comfortable with peace and quiet in his life. That said, I am guessing there is nothing you can ever do to make this VERY serious beanie situation (wink, wink) go away. Your best option is to try to negotiate the birdhouse for the beanie, but I am going to bet that when he learns it is not the original he will then make that the issue. I think he just needs a perpetual issue on which to focus.
I think they all create one. Mine had a thing for these air filters that were loud and bulky and old. (I used one when he was running in replay; coming and going at all hours. They blocked out the noise of him returning from his adventures in trying “to find himself.”) He bought them in the wild fires 10 + years ago. He was absolutely fixated on them and they appeared constantly in negotiations. In the final negotiations he mentioned them again and I gladly gave them to him. Pretty sure they are so old you can’t even buy filters for them anymore. They were SO important to him. How important? Afterwards, I went to clear out more of his left behind junk out of the garage and there in a corner was one more of those filters he just could not leave behind. He didn’t even know how many of them he had, hah!
If you try bartering and it fails, then my advice is just do whatever *you* want going forward because nothing is going to work for him anyway. It is a cathartic part of letting go or being dragged.
I do think you should muster up energy, strengthen yourself and go to the mats for your fair share. If you have to go to trial because he won’t be reasonable and you are paying and taking the time to do that, don’t go there to roll over. Let your lawyer fight like a junkyard dog for what you are owed.
Beanie (eye roll) ...
Me 41, H 47, M 15 yrs, S11, S13 BD 1: 11/4/14 we work on it; really I pretzel myself BD 2: 3/31/15 H goes down to "dorm room" 8/15: H back to MBR 10/15: H back in dorm room 1/18: H files, now divorced