Are you talking about donghyun he literally try to protect sooyoung in later chapters he love minhyuk but he discover that person he love was a piece of shit didn't like him and he was warning sooyoung about taesung not for his sex part because he is dangerous
Taesung is a gangster.... Ofcourse he's dangerous and Sooyoung knows that but he wants to know all Taesung's secrets and that's why he's trying to be Sherlock Holmes.... Sooyoung is not dumb, he also knows how much Taesung takes care of him and it was Taesung who saved him 1st btw.... So I don't think Donghyun has any idea about their relationship.. yes Taesung did fuck up that time but he regretted it...
Donghyun is literally just trying to warn him he care for sooyoung like a friend that all he not trying to get with minhyuk. Honestly sooyoung and taesung are flat character they really don't change throughout the story yeah they go through shit but that doesn't change shit about them ¯_(ツ)_/¯
Omg stfu so what about the sex you were having with Minhyuk??? Was it love??? As far as I can remember he used to choke you with his dick thinking that you were sooyoung and also used to burn you with cigarettes... Didn't he??? I just don't understand why are people so concerned about Tae and sooyoung's sex life... Both are adults and both enjoy rough sex and moreover, both of them like each other so mind you own business