Klint

You saw a diary on the floor, so you decided to pick it up and return it to the owner, but there's no name on it. Therefore, you decided to keep it.

The whole diary consists of how the man feels for the person he's infatuated with. It also said there that the person despises him.

You went to the store where you picked it up and asked the woman behind the counter who might own the diary.

The woman then pointed at the man who's rummaging through the lost and found. It was Klint, your enemy.