
I love how this author leaves some ambiguity to the line "That's definitely not love." It could refer to Heebum's feelings towards YooWon or vice versa. Therefore, in order to get a better understanding of their relationship, Jumi comes in and acts like a driving force for both of them to reexamine their feelings. By the end of "that summer," they would likely come to a realization about themselves as well as the thing called "love."
P.S: I'm not saying that Jumi is a driving force that pulls them towards each other again. Heebum could still realize that his feeling towards YooWon is actually dependence/yearning/obsession (anything but love) and that he loves Jumi romantically or no one at all.
He definitely knows after the night at the hotel. He’s acting cold towards Hakyung probably cuz he in doubt whether Hakyung is just pretending to like him since he would go as far as crossdressing as a girl to fulfill his role. Anyways best manhwa I’ve read. The storytelling, the art, the characters are just immaculate.