The inspiration sounds very much like Poe's "Cask of Amontillado" (as you say, don't do it, but if you are, it's the right way to!) This story very appropriately kept the horror lowkey until the end, and allowed the tension to build slowly but gradually. I suspected something was off about the pastor but wasn't sure quite what it was. Mostly, I like that Willoughby is shown to be a true coward rather than just a blackguard: he's quite willing for anyone else to take the fall other than himself, whatever he might say in his cups. Very intriguing and different take on the theme.
