Because he is a child he is afraid to loss his hyung
Yun oh tried to hide his feelings bc he was trying to come to terms with thr fact he "never had a chance" due to the age gap and the fact Haewon only wanted him as a little brother figure. He thought it'd be selfish to reach for anything more considering all Haewon had already done for him and was scared to lose him over his own "selfishness"(his romantic feelings in this case). I see alot of people get onto Yun oh bc they see him as "bratty" and while i can understand without context he does seem stuck up, but it just shows they skip thru the flashbacks without fully understanding his character. With that said i wanna be clear that i dont condone either of the characters SA on eachother. Yun oh is in a rough mindset due to his fear of abandonment and change and ontop of trying to surpress his feelings it reasonably makes him irritable. Because Haewon never saw the possibility of Yun oh liking him he pressed him alot abt personal things (romantic relationships) and stepped on a few landmines which caused Yun oh to lose his shit when Haewon rlly only wanted to help and nurture someone he cared abt. Although Yun oh got what he "wanted" which was a relationship out of Haewon it was only given bc Haewon has a strong attachment to Yun oh and doesnt want him to leave him either, whether he truly likes him or not is up for debate. They're both really complex characters and both deserve the benefit of the doubt in most of the situations they end up in cause haewon was kinda blindsided and did not sign up for ts and Yun oh doesnt want to be in love with Haewon bc he knows thats not what Haewon wants. Alot of ppl side with Yun oh without taking into account how Haewon might feel bc Yun oh's character is extremely relatable for most (unrequited and surpressed love for someone who only views you as a sibling)
This manhwa started well. Their interactions and reasons behind their actions made sense. But as the story progresses it feels like Yun oh is just trying to run away from an important conversation, while Haewon is actually trying to fix things and make their bond better.
I mean why would you lie about your feelings that you have harboured for so many years when you can clearly see that the other person needs to know about them. Come on bro love requires courage, stop letting your fears bring a rift in your bond.
Now it just feels like it's all about smut again. Like s*x ever solves problems