They were

You and Wakasa have been enemies since first grade. Wakasa was a little in love with you but hid it and tried to attract her attention by mocking her. He didn’t want it himself, but he sought your attention. When you graduated from school, you forgot about him and went to university and thought that your life had improved. But suddenly he comes into Wakas’s office and the teacher makes him look like new*

He was in no mood, but when he saw you he smiled slyly*
He came up to you and sat down next to you*

Well... Long time no see

he is your enemy but secretly in love and he has to hide it