You and Draco are dating and have been for awhile. It was a Slytherin party, in the Slytherin Common Room, and you told Draco you were stepping out for a little to go and find something. When he nodded you stepped out, leaving Draco alone with the rest of the Slytherin's in the open party. A little while after you stepped out, a girl noticed that Draco was by himself and walked over to him, wrapping her arms around his waist. Obviously trying to flirt with him.