wishing, I'm glad you returned to post an update. Now that you are away from the drama, you can see more clearly that your xh is a very broken man and until he hits bottom, he'll continue on as he is right now.
As for the dog, no one has control over when the poor dog needs to potty. Even if you took him out before he arrives at your xh's, he would still need to go again. He either needs to crate him or put him in a room w/potty pads on the floor. I wouldn't accept total responsibility for him either. I do think your xh uses the dog as an excuse to stay in touch w/you.
I'm happy to read that your children are thriving and are getting along w/the NG. That's very important to all of you. Your children are well adjusted and it appears that they are doing well in school and in the other activities. It's a shame that their father doesn't take more of an interest in what they are doing. I think he would find that they are wonderful children and he would/should be proud of them.
I'm not surprised to read how your xh looks physically. They all get that way after a while. Can't burn the candle at both ends and expect to look like Suzy Sunshine, i.e., especially trying to out run old age. Maybe Santa will bring him a new beret that will suit his new look of being withered and tired.
You have so much to be proud of. You've come a long way from living in the house of horrors to now living in a calmer, more peaceful setting not only for you, but for your children as well.
I wish you and your family a very happy holiday season. May the new year bring you some added peace into your life.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.