We can't fix other people. We can't force anybody else to work on any behavior that we don't like. For example, my own mother interrupts people and talks over them. Some people let her do this and Some choose to address it directly with her. Each person gets to set and manage their own boundries. If your boyfriend has a problem with your mother's behavior, it's up to him to deal with addressing it if he chooses to. If he chooses to just accept it, it's still OK. That's his choice to make.