You don't have to come every time. That concern of yours turns an act of mutual togetherness into something else. Ignore the dialogue inside your head and just enjoy the sliding around with your girl. It becomes a concern if you find you only come when you masturbate ... and before you get that far tell her you want to go down on her while you do masturbate - when it's time to come up for air show her the money shot
As for being concerned about being the rookie - just say thanks guys for training up the best ride of your life and enjoy what you've got for heavens sake!