Jisung felt the world around him becoming darker as he stood there watching you walking away.
He always thought wrong about you, he felt you deserved everything he did to you.
A phrase now stormed his thoughts "if a person laughs, it doesn't mean he does it because he is happy"
He had made a mistake, a serious mistake, maybe he deserved it, he deserved that as punishment, that you didn't forgive him.
You were right that day, he was regretting it.
Your diary made him realize. He began to read it simply for fun, he ended up realizing how much his behavior affected you.
"He can be handsome, but his personality is not and that makes him ugly for me"
Knowing that you would not forgive him, he still went for you. He saw pain in your eyes that day in the library, but egocentrism clouded its reality.
But if you didn't want anything with him now, it would be that way. It was the maximum he could do for you and maybe the last.