Okay so, firstly, Luhan is lonely. All his classmates do think he is caring and nice and what not. But they stay away from him for one reason. He suffers from a psychological disorder. They started avoiding him when he keeps mentioning Jongin.

Jongin was never real.

Only Luhan can see him.

Jongin was the first 'person' Luhan's mind created. It was an illusion to deceive him. To think that he has friends who do care. Because he is lonely, Jongin was created to be his close friend.

But the attention Jongin gave isn't as much what a boyfriend would give. Luhan desperately craved for love. Being brought up by grandparents who were strict and fierce, Luhan wasn't given any affection.

So Luhan's mind created Sehun. Sehun was everything he needed and wanted. With Sehun, Luhan became more livelier.

Of course Luhan was talking to himself in the library (in the first part of the story). Sehun wasn't there in flesh and blood. Same goes for the part where Sehun wasn't given a proper introduction. Luhan mentioned that Mr Kang didn't introduce Sehun properly. That's because he can't see Sehun. Sehun isn't real.

So were Chanyeol, Jongdae, Lay and the attackers. Even Sehun's parents were fabricated.

Chanyeol and Jongdae was created because Luhan wanted friends like that. Friends who can joke around. Jongin's more of the serious yet caring and dependable friend.

Minseok, Tao and Baekhyun, they're real. They are just momentary roommates. Once they found out about Luhan's disorder, they packed their bags and left. Except for Tao, he kind of stood by to protect Luhan for a while but he too left.

Once Sehun died, Luhan died deep down inside. He tried a lot of ways to kill himself off. He wasn't attacked by the group of boys associated with Lay. He was inflicting pain on himself. But on that evening, he was beaten up by some bullies from his own school. It was something like murder-for-hire. Luhan was the one who paid them to beat him up. Because he'd rather die then live without Sehun.

The oak tree was chosen as his death bed because Sehun died there. It was a special place for Luhan. Luhan believes that if he died there, he would meet Sehun. And he did.

Luhan was living a sad, depressing life. His mind just wanted to protect him. But in the end, it destroyed him. Because he still couldn't differentiate between reality and fantasy.