It's literally magic. Her calling out resurrected him, from being "buried in darkness". He isn't like a vampire like idk lestat from Anne Rice's novels, he is more like a force of nature, devourance, plague, death made by Satan from a fell sorcerer to go do evil shit.
It's like fairy rules, he was killed before by a maiden's sacrifice, a maiden called out and awoke him again, they are magically bound and her sacrifice puts him down again. Presumably until some new sensitive person awakens him.
He doesn't have a choice in his desire for her.
It is defs campy. Campy purple pros is essential to Gothic horror, it's part of what I love haha.
You just can't get that shit anywhere else. I'm a big fan of the supererogatory phrase