They sought to escape the power of flesh, the curse of being human. And their strategy?
Rituals of sex and poppy.

Here you earned my full attention. There's a good allegory of contemporary times.

Benjamin wandered off to his destination, ignoring her.

This is the point where I imagine there will be a cultists' carnage (writing this in real time, I still don't know the end).

“Melinda,” he said. “This doesn’t have to end with your blood.”

How come, no carnage? Mmh now I need to see that blood painting the cave's walls. I'm still confident about the bloodbath.

The first cultist stabbed him well enough.

Ok. Carnage granted. He's a supernatural being.

Benjamin gripped Melinda’s wrist. “Time to take a swim.”

My thirst has been quenched at last! But but.. here's the Dirgelian touch. He will sacrifice and drag his perverse beloved with him in the river. Nice, a dark-romantic ending which transports the reader in a perfect gothic Stokerian atmosphere. This is indeed the ending.