since everyone is guessing rn, i already had a feeling yoonsung already found out jiyoung/hakyung was a man when they went to hakyung's hometown, hakyung got drunk, and yoonsung brought him to a hotel. after they spent the night together, yoonsung’s attitude became cold toward him....probably because yoonsung tried to do something to drunk hakyung but ended up discovering the truth lmao
at the same time, i think he had already fallen in love with hakyung, so he didn’t know how what to do. not only conflicting with his feelings, maybe he began to distrust hakyung again and feel like he was betrayed. thinking everything he did with him was merely an act to fill his role.
after conflicting with himself, he tried to confirm his feelings by kissing him, giving him his clothes (which are technically men's fits) to wear, some panels zooming on hakyung’s physique from yoonsung's pov that isn’t like a woman’s.
then his cousin wanted to sleep in the same room with hakyung, yoonsung said no (hmm I wonder why if not he knew that hakyung was a dude). even though at the end the cousin sneaked into hakyung's room, hakyung chose to sleep on the couch instead, this probably made yoonsung realized that even though nothing about his is real, he is still genuinely a good person after all.
over time, after all that yoonsung finally accepted that he still loved hakyung no matter what, even though he’s a guy, and confessed to him after sending his cousin (or whoever she was) home.
(also, you can see a short-haired figure reflected in yoonsung’s eyes when he gazes at hakyung in this moment, also him saying "I give up, I like you more than I thought" something like that)
I want to bite him