This question comes across my desk often.  Generally speaking,
when two people sign a credit card application, there is a primary card holder and secondary card holder. Both are responsible for the debt. If the primary card holder later authorizes someone else to use the card, the authorized user is not legally required to pay the debt, they did not sign the credit card agreement and therefore, they are not required to pay. Authorized users sometime will find the Primary User’s Bankruptcy on their credit report. Credit card companies have this right but they more often than not do not report it. If this happens, dispute it with credit report agency.