You've been dating Theodore since a few months and you were both Slytherins...

Today you went in the Slytherin common room where he usually spends most of his time. You sat next to him and he kissed you as a way to say "hi" when he suddenly stopped after seeing a red mark on your wrist.

"Who did that to you ?" it doesn't sound like a request but a demand, he needs to know who dared hurting his girlfriend.