Keep it really simple. "According to my attorney, the house is community property, to be split 50:50 minus what I put in for the down payment. This is standard. The current value of the house is approx. X, it would cost Y to sell it, so if we sold, your half of: X minus my down payment minus selling costs divided by 2 is Z. I'm willing to pay you Z for your share and take over the house to provide D with a stable place to live."
As for where to stay when you visit D, I have located these inexpensive AirBnBs nearby, here's the list: Now that we are divorced I don't think it would be appropriate to have you staying in the house with me as that would be too confusing for D. I'm sure your girlfriend would also not be comfortable with you staying here with me.
Now - be aware - it's NOT standard to split the house cost that way, they usually do NOT take the selling costs into account if one spouse is keeping it, they just split the current equity. This is totally unfair to the spouse who is keeping the house but an attorney might advise him so. So the more straightforwardly you present it, the better the chance that he might bite and accept your math.
Also - sounds a bit like he is having a "moment" where he might be having a temporary regret. DO NOT BITE. He's just having a bad day with OW or a moment of reality hitting him in the face.
