I think that leaving you hanging, neither divorced nor married, is cowardly on your husband's part. If he doesn't want to be in the marriage, he should just say so. What he is doing is cruel. You can't move forward either to save your marriage or move on past the break up.
I agree with Mahonri. Your son probably knows more then he is saying. I would guess that in an effort to not take sides, your son is keeping certain things to himself. Maybe not an affair, but there is no way your son could live in the apartment with your hubby and not discuss this with him.