Sometimes in a relationship you have to be understanding of the other person's interests, and you can't control them on everything. Nor should you want to control everything. And also you can't be part of all their activities, because you both need to do fun things away from each other from time to time.
In this case, I think it is fair that it bothers you if he dances with other girls who are not his friends. It would bother me too. You could try to explain to him how that makes you feel, if it makes you feel jealous or insecure. Usually there are other things in a relationship that cause you to feel that way. Maybe he is not spending enough time with you? Or he doesn't give you enough romantic attention? Maybe try to deal with the roots of the problem in that way. You could tell him that it would mean a lot to you if you felt he listened and cared for your feelings.
Somewhere you should also question why it is he wants to dance with other girls. I think everyone dances with their friends (I dance with my friends who are guys, and it's just platonic). But if it's random girls, then it's another thing. Sometimes guys want to come across as "available" because they think it makes them more attractive to their girlfriends. It's a stupid macho thing they do. You could tell him that what you would find the most attractive about him is him, and how he cares for you, and not stupid boy games.
Hope that helps!
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