Can my ex refuse to pay for our son's college tuition even though it is in the divorce that we each pay 50%? He says he doesn't have the money and probably can't get a loan due to negative equity on his house... Is it worth it to take him to court?

If this is part of the divorce decree than take him back to court, he in is comtempt of the court order.

Consult the lawyer whom took care of the divorce; get his/her professional opinion on whether it is worth it. If your husband's credit IS shot, you son will most likely have to get a student loan to assist you with the tuition this year. When he applies for financial aid, only put the parent whom make the least amount of money down. If your ex-husband is making much, he may be your golden ticket to getting the financial help you need

Please keep an eye on the dates - this is over 3 years old, long dead. I'm sure the OP has figured things out by now.