You are on the hook as far as the creditor is concerned because you signed the loan.
Ah love, isn't it wonderful!
If the creditor does require you to pay, all you can do is take your ex back to divorce court and ask the judge to require her to repay you the money this loan has cost you. Bummer!
The divorce agreement, decree or judgment supposedly settled the rights and obligations between you and the former spouse. However, it does not change the obligations each of you had with third parties who were not in Court when you got the divorce.
The ex-spouse may refuse to make payments to credit card companies, car financing companies, mortgage companies, etc. Your ex may even file for Bankruptcy.
Depending on the law in your State you may have an action against the ex-spouse, and you may even be able to sue the ex-spouse if they file for Bankruptcy and have their obligation to you declared “non-dischargeable”.
Unfortunately the divorce or the ex’s Bankruptcy does not relieve you of any obligations you had to these third parties.
See a lawyer right away!
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Disclaimer: This answer does not constitute legal advice. I am admitted in the States of New York, New Jersey and Massachusetts only and make no attempt to opine on matters of law that are not relevant to those three States. This advice is based on general principles of law that may or may not relate to your specific situation. Facts and laws change and these possible changes will affect the advice provided here. Consult an attorney in your locale before you act on any of this advice. You should not rely on this advice alone and nothing in these communications creates an attorney client relationship. The opinions expressed herein are those of the author only and the fact that he has worked as an Assistant District Attorney; State Supreme Court Clerk; Special Assistant United States Attorney (Hawaii); Assistant Cornell University Counsel or Judge Advocate, United States Marine Corps should not be relied upon to assume that these statements reflect the policy of these organizations.