Unfortunately, there's no clear answer to this question -- but whether or not you are liable in the end, it will be a hassle dealing with this situation.

You have learned the hard way about what happens when divorcing couples fail to close joint accounts. If you have the money and the gumption, and if you didn't get notice of the bankruptcy, you could file a motion to reopen the bankruptcy and ask the court not to let your ex discharge the debt.

Or you might be able to file a motion to reopen your divorce case and have the court modify your settlement agreement so you get more money or property to compensate for being liable for the debt.

You probably will need to talk to a lawyer to do either of these things. But before you do, make absolutely sure that your name is no longer on any accounts that you ever shared with your ex.