At that point, things diverged sharply from the usual routine.
Priceless.
It was around the third time he had sex with Argus Filch that Severus began to suspect there was something seriously wrong with him.
I laughed myself into a coughing fit over this. Well done! Clever, well paced, funny and quite touching. I completely got over my ewwww, Filch reaction and enjoyed this portrayal very much.