What can you do if you co-signed on car and made the down payment and all payments to date and the primary took the car because you and his son getting a divorce?

You can motion the court for redress. It would be advisable for you to take all proof of payment to court with you and be prepared to show it. As the listed borrower on the note, he has as much right to the vehicle as you. However, if the vehicle is registered only to you, and you did not consent to the vehicle being taken, you could also report the vehicle stolen, and by whom.