Bad wording here, coercion basically means there's no consent. What happened rather is that Nanjo agreed to the conditions set by Mok-yeon, and even then, it's a bit of a grey zone and one could say it's basically coercion, a more lenient interpretation would be luring Nanjo in and Nanjo agreeing to terms he could've ignored altogether. Tbh, Nanjo at one point admitted to enjoying the sex, so I'm guessing he was curious from the start, but since he doesn't have experience with men and is probably dealing with some form of identity and sexuality crisis, felt like he could hide behind keeping the twink's feelings safe, basically using the whole 'lets fuck so I get the twink for myself' as cover for probably getting more curious about Mok-yeon and denying himself needs beyond trying to supposedly save an abused twink. Mok-yeon is definitely scummy for sort of pulling the consent out of Nanjo as he knew his feelings for the annoying lil twink and used that as leverage, but Nanjo is also a bit of a shady character as imo, he knew the twink was using him (and he used the twink to satisfy his own savior complex), but stuck around nonetheless and secretly maybe even enjoyed the weird threesome constellation they had going on. (I'm saying weird not cause threesomes are weird, but because of the complicated feelings involved between all of them, and especially between Nanjo and Mok-yeon)
The twink himself is the biggest opportunist in the situation, so I get the frustration with him. I don't think he's a bad person really, just immature af.
Yeah, basically this. We have three messy adults with shit communication here and Sunhwa really isn't that much of a scumbag imo (he wants a sugar daddy and honestly, in this economy, can't blame him; Nanjo tbh projected his savior complex onto him, and while Sunhwa could've cleared up the whole kinky shit Nanjo mistook for abuse, I also don't think Sunhwa wanted to actively portray Mok-yeon as a sheer abuser, why would he include him in the threesome in the first place then?), and I agree, if Mok-yeon was honest about it from the start, Sunhwa would've, indeed, just backed off or at least, wouldn't have taken it to heart as he was just a fuck buddy, not romantically involved with anyone. I think he was angry because it all happened behind his back.

Nanjo is no saint. Let’s please keep that in mind. They both had consensual sex as adults, even if it was coerced..Nanjo still agreed to the terms. I still believe ALL fault lies with that little twink bitch, who somehow, though not surprisingly, has decided to be a COWARD because he knows if he tells Nanjo the TRUTH of the matter (how he planned to squeeze him out of everything he could, for his own gain) then HE would look just as BAD, if not worse!!!!!! And that’s my take on it.