How do I get out of a car loan that I am upside down in?

I have an $18,000 loan on a 2007 car which is worth $10,000. My husband is the primairy on the loan and I am the co signer. It is my car and I make the payments. Except I can not afford them any more. $540 a month. How do I get out of this car with out my husband having issues. (we are separated and he is a really nice guy and I dont want to stick him with this when the car has been mine all along) Does anyone know what the loopholes are for this type of situation??? I love the car btw and would like to keep it if at all possible. It can not be refinanced because it is upside down and my credit is really bad (I allready tried) and I also tried to do an extension but they would not give it to me because I had more bills then money. FUNNY HUH!!