Oh maybe i'm not remembering correctly bc i did skim quite a bit in the beginning. I recall Sunhwa acting a lot cuter/sweeter to Nanjo, but I dont recall him trying to lead Nanjo into a fake relationship or expressing any false feelings/promises of exclusivity.
My understanding is that Sunhwa and Nanjo were sexual partners, and while Nanjo was soft on him, Sunhwa basically just kissed up to Nanjo so he'd get more monetary gifts. His personality is a bit fake but nothing of real consequence if Nanjo is giving out gifts without expectation of anything further.
i mean not really, you do realise that this guy is the one requesting threesomes right it isnt nanjo arranging them like cmon lol like even in bed he says please can you do more, you gotta realise nanjo just has on the craziest rose tinted glasses even mokhyeon in the last chapters acknowledges how their relationship only exists around nanjos delusions that sunhwa is some innocent guy, i dont think hes faking his personality- sunhwa shows care for mokhyeon evidently but why would he act the same around his 10yr fwb compared to the guy hes in a situationship with hes bound to act more cuter

I came into this expecting Sunhwa to be a major problem, just a tool to get the relationship going, but honestly he's not bad. He has his own social circle, is fairly upfront, and even cares about others like Mokyeon. It's very much just about the physicality for him and i like that he's honest about it.