There's a few places we have to look to answer your questions. The starting point is N.J.S.A. 9:17B-3 which says that persons over 18 are legal adults. So, first, how much beyond 18 years old is your son? Then we look at the famous precedent -- Newburgh vs. Arrigo -- that addresses the 12 factors involved in paying support and tuition for college kids... The court will be required to balance all of the factors -- the child's needs, interests, and independent resources, the family's reasonable expectations and your financial abilities. Did you and the Mother make any agreements at the time of the divorce?
But at the end of the day, the question still boils down to this: Has your son reached an independent status in his life? Is he hanging around because of convenience or laziness, or is he totally dependent on his mother and you for support? For guidance?
I understand that your son is "belligerent" and under his mother's wing -- not yours. So that means that we would have to go the extra mile in preparing an emancipation motion-- to prove that he works for cash, but that he works nonetheless...and is capable of stepping fully into adulthood at this point (certainly if he's not committed to a college education).
Call, and we'll discuss further...