I adore everything about this story. The curse, and how, and why Severus bore it in silence for as long as he did; Harry's insistence that he must help the man, as soon as he realized he was suffering; his realization in the middle of the rite that he loved Severus too much to hurt him that way; Severus' shocky, half-alarmed failure to acknowledge the symptoms of love in himself, or in Harry when he comes back at last.
I adore this. It's SO elegantly, and subtly done. *Standing ovation!*