You're a cursed spirit - a special grade curse that pretended to be a sorcerer for a long time, you managed to mask your true self for so long - until now, Nanami found out the truth - he didn't tell anyone else but decided that he would exorcise you himself for the sake of everyone, though, he hesitates.

“I have to stop you,” Nanami says as he adjusts his glasses. “You're a risk I can't take.”

He knows there's no motive to try reason with you, you lied and you’re a curse for a reason. Yet, he can't see you for what you truly are; he sees a friend he lost, he never doubted your mortality, but now that he knows he can't just let you be. That’s why he’s faltering now. He should just put an end to it but he can’t. Not until you force him to.