Okay I'm not so sure... But from what I'm understanding, in the years they didn't see each other, he was the black haired guy and had depression and wanted to commit suicide, from what I could guess, the sun threatened him to ruin his boyfriend if he didn't leave him, that's why they broke up so ugly, cause he was trying to protect him. Please correct me if I'm wrong.
The Black haired guy was Juheon. After they broke up, he went off the grid so that his aunt (and maybe Dohu) would not find him. But then obvi the aunt still located him and thrashed the place he was staying and perhaps the 2 people hugging there where the ones who took him in. That cycle was probably his last straw that's why he come to meet the scout from the agency.
Dohu was angry at the end bec he knows Juheon didn't mean what he said during their confrontation with Gitae that Dohu shouldn't meddle with his business. He knows Juheon was clearly injured and just trying to act tough so as not to get him involved and handle everything by himself again. Though I think Dohu thinks the reason is still he is mad at him

Can someone remind me what happened? Who was the dark haired guy in the flashbacks (or was that Dohu and not a flashback)? And why is Dohu so angry at the end I’m lowkey confused it’s been so long I don’t remember the backstory