What are you confused on?
I can try to help
So Hajin already knew the twin before? I literally don’t remember that. And why is the other brother being so dodgy?
Hajin learns about the twin chapter 18. Chapter 19, He was told the twin was the teenager Hangyum he knew from the past. But the idol is really the teenager from the past. Hanwool as Hangyum meets Hajin for the first time in chapter 27 and 28. Chapter 39 is when Hajin is meeting Hanwool as Hanwool. Hanwool is being so dodgy because he pretended to be the Teenager Hangyum that knew Hajin in chapter 27 and 28. Here he is being introduced as Hanwool and exposing Hangyum's lies.
Oh... see I forgot all of that
I need to go back and read some chapters again because I’m so confused