I'm not really sure yet...
Our close friends know the score and know that they are my husband and boyfriend.
However, our living situation is about to change. For simplicity's sake (as we're moving back into the town where my mother and my husband's mother live) I think the boyfriend will be assuming the "roommate" role.
They do refer to each other as "fraternity brothers", but it's very silly and tongue-in-cheek.