Hang in there, and don't get too discouraged! It's more important for kids to have and maintain a single friendship than it is for them to be well liked by all their classmates. And some people will just naturally be more bossy than others (we all know bossy adults, right?) If they learn to focus that behavior well enough, "bossy" turns into, "natural leader."
My daughter had the same problem. When she had a friend over to play, she would announce that, "We're playing this!" without asking what her friend wanted to do. If she had decided to play dolls, she would take whichever doll she really liked and announce, "This one is mine. You play with this one," and hand one to her friend. She would often even dictate what the dolls did - "Mine says this, then yours says that." I would pull her aside over and over (and OVER) and say, "Ask what she wants to play." Every time, my daughter would stare at me like I was a crazy person and say, "It's MY house! I decide!" When I told her that she should always give her guest first choice of toys or videos or whatever, she'd say, "They're MINE! I decide!" Then she would often literally be in tears because she felt like, "No one likes me!" We tried explaining, we took her to a counselor, and nothing really improved. It took her into her teens to start to change, and then she went too far the other direction, and tended to let her friends call all the shots even if she knew it was breaking the rules and they'd both get in trouble. (She informed me more than once, "No one will like me if I have to follow all these rules!")
That's my very long winded way of saying, keep explaining why you ask for certain behavior, and why other behavior alienates other kids, but your son will have to figure this out for himself. It might take years for him to do that. Figuring out interpersonal dynamics is easy for some people, and very difficult and confusing for others. What is SO OBVIOUS to you will sound TOTALLY alien to your son.
My daughter is now in her early 20s, a delightful young adult, but she's still occasionally puzzled by the complexities of what's good manners vs. being taken advantage of, or how to make decisions as part of a group. That's just who she is. We taught her - now it's her job to put it all together and use the information.