He doesn't get much sleep, that night. In the end, it's only because his transformations tire him out that he manages any at all.
Should he tell his mom? Yes, obviously. Vampires are real. Of course he should tell his mom, she needs to know not to go out at night. He doesn't know how many vampires there are but he no longer trusts the official statistics on the number of deaths and disappearances and so none of his old thought about how dangerous things are hold water. Daytime excursions only.
Does god exist? If the cross thing is real probably. Unless the whole world has a belief-based magic system or something. Of course, the first thing he'd do is spread fake weaknesses, if he was a creature of the night not powerful enough to rule over mankind in the light of day, so he's not going to rely on the cross thing at all.
He hopes there's an afterlife after all. Maybe if there isn't people could build one, eventually.
The whole world is suddenly a different place.