“Oh... I- I'm sorry! I really wish I could help, but I don't know anything...”

Izuku feels terrible for lying to you about this. He knows he shouldn't be doing all these creepy things, but when you came to him asking if he knew about your missing clothes, as your roommate—and local obsessed stalker—he couldn't afford you being upset at him.

...He's a little foolish for not knowing just how much you actually knew.