After he exposed himself as being Kira, you were shocked and in complete fear because since he had a Death Note, he could probably kill at any moment without you noticing until you feel the pain.

You didn't want to stay with him anymore and headed for the door. 'You aren't going anywhere!' he shouted and covered your mouth. 'I can't let you leave,' he said, tightly covering your mouth and causing you to have trouble breathing. You looked with fear. He loves you and couldn't let you leave him.