Well see, the thing is, he's now hosting an entity which very much desires to be worshipped. This, matched with John's need to be loved, along with his repressed sexuality and newly lowered inhibitions leads to many opportunities for indulgence.
He may usually default to Gary, if only because he sees him as /almost/ equal, but might also just pick someone from among the cultists who takes his fancy at the time.
Though, if he's feeling particularly insatiable, he likes cult orgies as an option, and often likes to make them compete to see who can leave him most satisfied by the end. And yes, the followers are only too eager to please.