M.B.
He sounds like he is in a zone of proximal development. He knows but isn't quite there. That is were we come in as parents. Just remind him that he can do it, and try to be as consistent as possible.
Pull ups usually drag out potty training, because children have a crutch to use. Also, remember that it is also harder for the little ones in the winter time.
I used a book called Once Upon a Potty. I like the book, because it does not make it a game and fun time like most books. It helps children understand their body and what it feels like when they need to go. It has been around for over 30 years, so that speaks for itself.
Hang in there--you both can do it together. And, if you find some interesting information, I would just pass it along to his father--in written format. That might help. I also have a son who visits his father and written format helps with us the most, because we generally can not get along.