I always approach AR stories with great care, and stories with religion with even more care. So many writers get the letter of religious law correct, but miss the spirit.
But this? This is something that I will read again and again.
Not just the vampires - which made my heart go pitter patter just because ... vampires! - but that you gave Severus his choices and let him take the hard road down the middle. Neither abandoning his faith because it couldn't give him what he wanted nor abandoning his lover because he didn't fit with his faith.