Pndm, I feel ya. I'm yet another with a very similar situation as you know from your comments on my posts.
My AH also tries to get me to continue enabling, pushing by not committing to a visitation schedule, spending as much time as possible at our apartment because his current living situation is "unbearable", not dealing with the fact that the divorce IS happening so he won't answer me on if he will sign custody orders, won't figure out a better living situation, won't discuss how to best split our financials.
Yesterday he came over with his back completely out and spent the day laying around the house with a sad, sad victim face while I took care our daughter. When I offered to give him a ride to his home, he told me that he "needs my help to take care of him" until his back is better. He had brought stuff over assuming he'd stay over. When I told him no, he was totally shocked and angry.
Anyway, I've tried the loose schedule as well, I've tried to reason with him, but it's all for naught. The most helpful thing I've heard lately is that I'm acting as if I'm dealing with a rational person and that is so far from the truth. Just that fact has helped me see that there is no point to conversations, that I am going to have to draw a hard line, that I will have to go through the courts to get any decisions made and I'm going to have to deal with the fact that he will view any actions I take as utterly horrible and play the victim. It sounds as if you will have to do the same.
All my best to you. You are doing the best you can and you are doing what's best for you and your son.