Many married couples often feel they are automatically responsible for each other's debts. This is simply not true.
You are of course responsible for your own debts. However, your own debts may or may not include your spouse's debts. It depends on whether you have co-signed any debts together. For instance, if you bought a car together, you may both have signed for the loan.
Also, if you live in a community property state (Arizona, California, Idaho, Louisiana, Nevada, New Mexico, Texas, Washington, or Wisconsin), you and your spouse are jointly responsible for each others' debts incurred during marriage, even if you did not "co-sign" for the loan.
In order to file a joint bankruptcy petition, you must be legally married. Living as co-habitants does not allow you to file joint bankruptcy. Most states do not recognize common law marriages or same-sex committed relationships as valid marriages.