I think his parents found out what happened
Sunho (S) was uncomfortable doing sexual things I think but felt that he was forced into it as Doyun (D) would’ve left him if S wouldn’t do it? But D didn’t know he was uncomfortable with it and pretended to not need S so that S would always chase after him. Then it got too much for S as ppl discovered their “shed” and was talking about how disguisting the culprits were, D didn’t care and ignored it where as S was shaken up by it and got into a fight.etc and that’s where it all went downhill (that’s what I’ve gathered... I’m really bad with names so I just use their initials, sorry!)
Basically...Miscommunication
But wasn't Sunho crazy about Doyun? it's not like this was ever a "normal" friendship. I got the feeling Sunho's parents were very strict or his environment and that's why he thought something like having sex with a man was "nasty". I don't know. At a very early stage of this story I was convinced Doyun raped and bullied him, but that wasn't the case. I thought Sunho was surpressing his urges and now the contrary happened and he became a rapist. No idea. I'm lost here. Thinking back Sunho is the crazy psycho and Doyun had just bad luck.
Was there ever given a proper explanation to why this relationship didn't work out in the past? Sunho was just too clingy and, well, not sane. That was it? Did I miss something? Apparently Doyun didn't care enough, but wasn't it Sunho's fault to begin with? He thought it was nasty what they did, but Doyun didn't force him to sleep with him in the first place. I'm confused ...