The way I see it is…

Daon never had someone to take care of him growing up so he’s emotionally vulnerable to love bombing and any acts of kindness. That’s how Jaemin manipulated and basically groomed him. Soohyun was dumb to agree to pretend to date Jaemin, but with how wholeheartedly Daon believes Jaemin, Jaemin could easily tell Daon any lie to get him to distance from Soohyun. Which I guess is how the author explains Soohyun going along with Jaemin’s fake relationship plan but I still think there was a better solution for Soohyun to win that fight. Cuz how the fuck did you expect Daon to grow feelings for you knowing you’re dating his idol lol. Bruh the only reasonable person is Sunghyun. What I really like is how when Daon is with Sunghyun he’s not some poor begging kiddo… he gets to be who he worked hard to become, a successful and independent individual. When he’s with the 2 hyungs he keeps reverting back to being the indebted one all the time.