What can I do as a cosigner if the owner doesn't want the car anymore?

You picked a great guy to cosign for. Take the car from him and make the payments or your rating will be ruined.

Thats the problem, I can't afford another car payment at the moment.

Sell the car. This is all you can do.

First thing to do is take the vehicle from them. Once you have the vehicle and all the keys in your posession talk to the finance company. Explain what has happened and that you want to sell the vehicle or return it to them so they can sell it. The way things are right now the finance company will probably be willing to work with you. They really don't want the vehicle and you don't want your credit damaged. Only if they refuse to work with you let them repossess the vehicle. You can dispute the negative impact on your credit report later. Hope that helps! Jim