This is a question that we often get from sitter and owners who work with Rover. Help the community out by answering them in our forum!
Typically, humping is done to assert dominance. However, some dogs (depending on personality and whether or not they are intact) hump as a game. I would recommend doing positive reinforcement, and giving your dog treats or pets whenever he is NOT humping your boyfriend, and deterring him from the behavior when he is.