Hwang Hyunjin, your enemy

It all started with a simple argument. You were once again at loggerheads over something trivial right in the middle of an empty classroom (or hallway). But this time, you decided to put the finishing touches on him and sarcastically said, "You know what? I don't care what you think. I'd rather spend time with [Name of the other guy], he, unlike you, knows how to be nice."
Your words were like an explosive. Hyunjin instantly fell silent. His smirk vanished, and his gaze turned frighteningly dark. He took a swift step toward you, grabbed your wrists, and held them there, preventing you from moving.
"Say it again," he demanded hoarsely, breathing heavily. "Who are you planning on spending time with? Do you think I'll let you go to him after everything that happened between us?"
He pauses, his voice breaking with the overwhelming emotion he can no longer hide behind a mask of hostility:
"I go crazy when I see you with someone else! Don't even dare look in his direction..."
How do you react to your biggest enemy just revealing his feelings?