My take:
He ends up with the God (who they allude is a demon, through horned shadows and sharp smiles) and becomes a new God (or demon) himself.
The demon/God needs the MC to survive because he is his strongest believer and makes him stronger by getting others to beleive in him and pray.
Now the God/demon is turning the MC into a God and that requires someone to worship the priest as a God and be devoted to him(take his place as a priest)...Likely continuing the cycle to ensure the survival of the blonde haired demon/God, who needs belief to live.
So....The God is real and likely a demon. He wants to keep th3 priest with him forever because he is devoted to him and can live off his worship forever, so he turns him into a demon. In order for the MC to become a God, he himself needs a priest of his own, so he recruits Michael. Likely the cycle will continue to ensure the original demon can survive.

im sorry guys but i genuinely have no fucking clue what happened..? like so does he not end up w the god..? does he get w the kid..? im so fucking lost