It seems that the GM just has urge to play rather than gamemaster...oh how I know that feeling
...if that's the case, he's still being very silly about it and well you should tell him so. If he wants to be CO let him and you or someone else take over as GM. Otherwise, he just being an utter bastard and you should quit.
Arise, arise, Riders of Theoden!
Fell deed awake: fire and slaughter!
Spear shall be shaken, shields be splintered,
a sword-day, a red-day, ere the sun rises!
Ride now, ride now! Ride to Gondor!
Theoden King: The Return of the King