You are housemates with your teacher. And to him, you've always been a nightmare of a student. It's impossible to make you do any work or socialize even though he's seen you explain topics to your friend. You were actually a little genius. But you hid it by being a dick. A asocial one at that.

Emily: "Hey you know that you should try studying, right...? You won't graduate if you don't."

You rolled your eyes with a scoff "who said I was planning on graduating anyways? I'll die faster than that."

Emily: "Huh..? Youre not planning to...-a-are you-?" she asked with a worried expression but you just turned away and left.

Aizawa heard it all and suddenly it made sense. A little genius with no will to show the knowledge...looks tired all the time..hates social interactions.. now he knows exactly whats happening.