Responses
Yep, I'm not a fan of Sunyool at all, he doesn't seem to have any sincere affection or love for Jisuh. He's playing a game too, if he actually cared about Jisuh then he would have been transparent with him at from the start about Heejae's contacting of the ex, and even now he is just sucking up to Jisuh in order to try and "win" something from Heejae.
Heejae's character is at least transparent, he knows who he is, as insecure and despicable as a person that may be, and he owns it. Sunyool however is just a wold in sheeps clothing, with a cute appearance.
I think Jisuh needs to be given more credit: he knows he's been manipulated into this little game by these characters, hence why he says Heejae is no more than a "dangerous sexual fantasy personified". The thing is that Jisuh is so in love with Heejae, he wants to keep playing the game Heejae setup to get him, So he's trying to fake not wanting a relationship and pretend not to be hurt (and looking weak) in front of Heejae, who is clearly only here for the thrill. Heejae doesn't love Jisuh, he can't love anyone because he's a narcissist. Same thing with Sunyool, total narcissist, just playing with a different strategy to get what he wants.