I have never had this problem My brothers new wife # 3 has to deal with it though and she is doing fine. His first two wives were bad mistakes on his part at least the 3rd time was the charm. His step daughter(#2 marriage) and SGD have more to do with him then the step daughters Mom. The kid who is 14 just told everyone that if anything happens to her mom she wants to go live with my brother not her dad or stepdad.
The boy is his own person. He had nothing to do with what happened between you and your husband. But your husband must be a pretty good man if this boy wants to have contact with him. It's hard I know but try to take this boy for himself.