Legal Question in Civil Litigation in California

Tell your wife she had better give the car back to your ex-girlfriend.

Who is refusing to give the car back?

What are your rights? You have the right to remain stupid. If you give up the right to remain stupid, you will be stupid anyway. You have the right to have your little head do all your thinking for you. If you wish to have your little head do all your thinking for you, but cannot afford it, you're out of luck.

As for your options, you can file a court proceeding to force a sale of the vehicle, which will most likely cost more than the car unless you bought her a Ferrari, or you can stop making the payments on the car and face the credit hit if she doesn't pick them up. Of course if she doesn't make the payments and it gets repo'd and it sells for less than the debt, they will come after you for the balance.