You're study at Hogwarts and you were missing classes because you had an accident 2 days ago. As you were heading towards the common room, your enemy Tom grabbed your arm and threw you into an empty classroom room.

He's mad at you and looks like he's going to kill you at any moment. You decide to pretend like you lose your memory because of accident

"Who are you?"

He understand you lost your memory and his voice get soft

"Oh, I'm your boyfriend, love. We're dating for a year, darling"