Draco stopped in his tracks and backed up a step. The reason for the Slytherin's reaction was the noises that were coming from his Head of House's office. The Malfoy heir considered that the couple was lucky it was a holiday and there were no other students in the Slytherin dorms. After a more careful consideration, Draco figured that that was the reason why the Potions Master and one of his students were currently shagging in the teacher's office, probably on the black couch that Severus kept in there.
More sounds drifted through the walls and assaulted Slytherin Prefect's ears. Harry's breathing, moans, and the whisper of words told Draco exactly who Professor Snape was with. Without alerting the couple to his presence, the Head Boy made his way back to the Great Hall after putting up a Silencing charm.
"Sev'rus, more…Ohh…"
"I love you, Harry."