I don't understand Seunghyun's behaviour at all, in the flashbacks, he's very much aware of how awful this industry is and that neither of them can be happy as long as they are a part of it. Tf he's being so weird about after all these years? Something big had to happen after he left Japan to make him this way. He knows damn well Yuta didn't choose this life but he's talking about "consequences of [your own] actions". Honestly, this sounds like he's coping because deep down he knows it's all his fault.
Also, he's bringing up old men and how young Yuta is all the time, so it definitely bothers him :/

The amount of time Seunghyun mentions old men, it definitely kinda bothers him
He has yet to realize how mentally broken Yuta really is and that he needs to stop saying dumb shit to insult him cuz Yuta gonna do it for real
Gonna take Yuta almost dying and in the hospital again for this dude to wake up