He knew exactly she wasn't coming to his office only because of the essay or academic issues. The way she always exposes herself in front of him. No body needs to tell him that she is interested in him.
He himself was not left out. He's equally more than interested in her but he wants trying as much as possible to pretend. He doesn't want to have anything to do with a student. He sees her as a small lady and a teacher was not supposed to be in a sexual relationship with student.
If anything happens, it going to ruin his reputation. Apart from that, he feels she's too...