Renter's insurance only covers the named insured and resident relatives. This usually means the named insured’s spouse and/or children. Your specific renter's insurance policy will list who is considered a resident relative and how they would be covered on the policy.
Roommates, boyfriends, and girlfriends are different. They would not be covered on the policy unless they are listed as a second named insured. Some companies will allow a non-relative to be listed as a second named insured on a renter’s insurance policy, but not every company does. You would need to check with your agent to see what your company allows.
What is the risk of adding a roommate, boyfriend, or girlfriend as a 2nd named insured? Any claims that are filed under the policy go on your record too - even if you didn’t have anything to do with the claim. If your roommate/boyfriend/girlfriend files a claim, such as theft of property, this would go on your property insurance record as well and could affect your future insurance rates for up to 5 years.