Blurry lines: "Where's Nol right now!"

It seems like Nol was part Kou's friend-group until "something" happened, to which Kou took no responsibility for citing the excuse that he "needs to rise to the top"/"they don't understand". Nol's shadow was behind his friends while Kou stood between them & his parents.

So did Kou do something to Nol publicly in-front of his friends and run-off....Did he put up the front of a decent-brother only to reveal a hidden motive? Nol did say that Kou did "betray" him. Clearly Hansuke and Yu Jing know Nol...to the point where Nol can call Hansuke a wild-card and know Senator, Yu Jing's dog. Also Hansuke automatically wanted to invite Nol to the club ( he's underage tho ), and the amusement park when hanging out with Kousuke.

Also Hansuke on several occasions have made under-handed jokes about Nol's Kou relationship. In addition, Yu Jing is also very aware of the brother's friction towards one another. Yu Jing describing him as originally "meek".

Essentially what ever happened between Kou's friend-group is related to Nol...

It also seems like Kou's friend group found Nol endearing enough that they were concerned about him when something happened