Can father refuse to pay for college costs

Can I refuse to pay for my 18 year old’s college expenses until he gives up his now-regular use of pot which caused him to be expelled from high school in December? My divorce decree calls for me to support him for 4 years of college but he is currently expelled from school for his two possession offenses during his senior year of high school. He is still openly using pot. He is currently completing class work to be able to earn his high school diploma in June. His mother is threatening to sue me for “preventing him from his college experience.”

I would read careful what your legal agreement is in terms of “college costs”. Did you agree to pay only for tuition? Are you paying for all college costs including board, books, miscelleaneous expenses? Are you paying every semester? Would you be giving money to your son or to the university?
It sounds as though your son is trying to get his act together. He won’t even be able to apply for college until he has his h.s diploma so why threaten…why not just wait and see what transpires?
If he does manage to get accepted to a college then you will have to cross that bridge when you come to it. Perhaps you can work out some other incentive based on what you have in your agreement.

I would have to see the specific language of the Order. If the Order directs you to pay for his college expenses and he is not currently enrolled you would have no obligation to pay those expenses. As for child support, you are still on the hook according to the law since your son is in fact making progess towards his high school graduation.