Question

Texas. I am about to get married. My fiancee has been married once before. Their divorce decree states that she should pay one of her ex-husband's student loans. She could not afford a lawyer at the divorce and signed it to get out. After the divorce her ex told her not to worry about the loan, he would pay it. That was 4 years ago. When I saw the divorce decree I felt like we should have an attorney look at it. My future wife instead called her ex to talk it over. Her ex has remarried and his new wife naturally would like my fiancee to start paying the bill. She sent an e-mail, and in it confirms that the ex husband did tell my fiancee that he would pay the bill "until she could afford to pay on it". The loan is in his name and does not show up on my fiancees credit report. What am I on the hook for here? How binding is the divorce decree? Would her ex have to take us to court to get the money? Does the e-mail his new wife sent show a post nuptial agreement?