I don't understand korean so this is what a I got from just looking at the drawings and translating a few panels:
Protagonist and his crush have sex, I don't know how they got to that point. Ah-In isn't seen for a few chapters after the amusement park, he's embarrassed of what happen I think (not sure).
The brother looks also kinda twisted and obsessed with the protagonist.
MEGA SPOILER ABOUT THE PROTAGONIST PAST :Ah-In wasn't the one who shared the fake picture of the restaurant food but it was another guy, so Ah-In is innocent :(
This is what I understand until chapter 40
(sorry for my bad English)











Was not necessary :/