If I have health insurance but my spouse does not, and he becomes ill or injured, am I legally responsible for his med bills?

The answer is "it depends." As a general rule, individuals are not liable for the debts of another unless they agree to pay them in writing. However, there is a common-law doctrine called "liability for necessaries" under which the spouse of a needy party is liable for food, clothing, shelter and medical costs for that person, assuming the spouse can afford them. These claims are rare but technically possible.