Yes, XH is being a complete jerk. No doubt. But you have launched into rehashing and emotional blackmail in what should be a business deal. The button pushing is definitely not one-sided here.
You are throwing a bunch of random stuff at XH that is totally inappropriate. The mention of the card, the "bringing us closer together" line, and so on and so forth. You are trotting the same old sort of stuff. Why? Make him see the light? Whatever your goal, change it. This is really where things started to escalate. Just stop. Focus on the business.
What exactly is the arrangement with the hot tub? Does your divorce settlement say who will sell it? Does XH have the right to sell it without your agreement?
Right now, you are quibbling about $400. This is so NOT worth it. If he sells it for $1600, then he would get $800. You have $500 available. Ask your tenants for a one-time $300 hot-tub premium and be done. Or, give him $500 and ask him to take $50 off support for 10 months to give him a total of $1000. This gives him $200 more but spreads out the cost to you. Whatever. Focus on the financial arrangement.
Also, you are effectively asking for him to give you $400 for a luxury item. This is not reasonable, nor should you expect it. How much are you willing to contribute to the upkeep of his swimming pool? It would be unreasonable for him to ask you to do so. How would you feel if he tried to emotionally blackmail you into reduced support so that he can better maintain the pool and get a new slide for it because the kids would enjoy it. No way. Same with proceeds he can get from the hot tub.
That being said, again, XH is clearly being a jerk. Zero surprise there. If he refuses $800 when that is all he would get from the guy he wants to sell it to, then you should look closely at the actual divorce settlement to discern your rights and weigh your options carefully.
"XH,
The offer you are considering would put $800 in your pocket. I propose the following so that you will benefit equally: __________________.
Alternatively, I will trade your labor for the AC service for your share of the hot tub. This might be attractive as it is a quick way to tie off two loose strings at once. So, you give me your share of the hot tub and I will take care of the AC.
