Ex Husband Wants To Keep A Car Loan In My Name

I am in Texas, if it matters. So long story short my ex husband and I are recently divorced and one thing agreed in the divorce decree is that we would sell the car we shared that has a loan in my name and split the remainder due on the loan (about 6k upside down). Neither one of us wants to have to pay that much at once and he is willing to keep paying the loan and all expenses on the car if he is the only one driving it. Am I silly for wanting to do this as well? I have access to another car so that is not an issue. We are amicable and friendly and both seeing other people already. Should I draw up a contract stating he agrees to pay it each month until we sell it? What should the contract say? Should I get it notarized?