If your ex-spouse has filed a chapter 7 and if you are a co-signer with your ex-spouse on a debt, the creditor can normally require the entire payment of that debt from you even though the divorce decree assigns the debt to your ex-spouse. The provisions of the divorce decree are not binding upon creditors. Depending on the terms of your divorce decree, however, non-support debts ordered to be paid by the ex-spouse under the decree may not be discharged.
If your ex-spouse has filed a chapter 12 or 13, the "automatic" stay extends to any individual co-debtor that is liable on consumer debts with the debtor [11 USC §§1201 & 1301]. In order to pursue collection from a co-debtor, the creditor must file and prevail on a Motion For Relief From Co- Debtor Stay using LBF #s 1220 and 1220.5 for chapter 12) or LBF #720.80 (for chapter 13 see also LBF #720 (Notice of Motion) and LBF #720.50 (General Relief From Stay Procedure). In addition, a chapter 12 or 13 debtor may be able to discharge non-support marital debt ordered in a divorce decree, even if it is not dischargeable in chapter 7.
As this is a very complicated area of law, you should seek legal advice from an experienced bankruptcy attorney for a thorough explanation of your rights and obligations in this area as soon as you find out that your ex-spouse has filed a bankruptcy.