D.T.
You and he need a "date". You need to sit down with him and him alone. You need to talk to him and listen to him and have an open mind and heart.
Since he's been "girl" focused since 3, I'm tempted to say he's ALWAYS going to be. He needs a safe place because the world is going to be cruel. You need to make his home life as open and as welcoming and loving as you can. He needs to be able to be himself, if that means make-up and nail polish, then you need to give in.
You can put conditions in place, he's still a kid. You can let him dress up all he wants at home, but not out of the house. You need to tell him the truth about what he'll face outside of the house if he chooses to go "out".
He MAY still yet grow out of it, then again he may not. You need to decide now what kind of parent you're going to be and be it.
Good luck!