Am I liable for the debts of my partner?

No, unless you have specifically assumed responsibility to pay a particular debt - such as by cosigning a loan or if the debt is charged to a joint account. In contrast, all debts incurred during a marriage are considered marital debt, for which both spouses are generally liable, even debts incurred by the other person. The only exception to this for unmarried couples occurs when you have registered as domestic partners in a location where the domestic partner law states that you agree to pay for each other's basic living expenses - meaning food, shelter and clothing. This, of course, would not be the current state of the law in Michigan.