This is now the second time that MC bro has told Heewon the cold hard facts about his misplaced romantic expressions.
It always was the case that Heewon's one sided feelings for the brother wasn't love. It was a case of having a crush at first sight, mistaken belief about the identity of his fated lover + internalised shame after learning that Hangyul who was still attending middle school at the time was his actual fated lover.
I really hope this puts the nail in the coffin of their ship, it was never going to sail. Not when there's still a 1% chance that Heewon finally comes out on top over eunshit and reclaims his and Hangyul's future by reconnecting their thread