Heather, It's the holiday season. Even though he's not been around much for the holidays, he's thinking about what he had and what he doesn't have any longer. Some do reach out at this time of the year and then disappear again around March 17th.
I know you want to be kind, but you need to disengage w/him as much as possible because you don't want to go back down the rabbit hole again. Keep the conversations to the girls and only respond if it's something you need to respond back to him about. As for the dog...just idle conversation and he wants to keep you on the hook.
You are doing great and I do not want to see you go backwards!
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.