Is ex-fiance's liability for auto loan

Please note that this is not legal advice and does not constitute an attorney-client relationship.

Based on the facts that you provided, it would appear that he is the owner of the vehicle, even though you have been making the payments. This, however, is a very simplified answer.

Have you considered attempting to find personal financing and purchasing the vehicle from him (perhaps at the current payoff value of the lease)? Or, if you are on good terms, you could enter into a written agreement with your ex that you will continue to make payments on the vehicle, and when the vehicle is paid in full that he will transfer title.

This is probably not an issue that you would want to litigate, as the time and effort will probably be in excess of any benefit. You may want consider trying to work out an arrangement without the involvement of attorneys.