Car instalment behind?

Hi i need help my car installment is two months behind.I bought the car for my ex and he is just paying whenever he wants to. i told him that he must bring me all doent so that he can buy the from me trough the bank. i am just scared that the bank is going to repo to car and then ill have a bad name. how long till Ned bank takes back a car that has no been paid. or what can i do to get this car of my name can i give it back to the bank. help needed urgent!!!