Nicely summerized. Wow I didn't know people talked about Nanjo like that on insta, I'm not on there or on twitter... That's for the better I guess.
I totally get feeling sympathy for Mokyeon, especially given the fact that :
A) he is the main character and the ONLY character whose thoughts we have access to. Very important factor for why people feel for him
B) the narration does its absolute most to make us feel bad for him in spite of his terrible choices : only following his point of view, internal rationalizing, putting his sad backstory as the first chapters of S2...
So yeah I get feeling bad for the guy, he does look pathetic and pitiful spiraling like that... Alcoholism is not a joke and one hell of a disease. And as you said, bpd is not a joke either (he's clearly showing symptoms)
Still, no matter how much Mokyeon is going through it right now, Nanjo has 0 obligation towards Mokyeon, as blunt and harsh as that may appear.
Yes Nanjo has been shown to be quite naive and very obtuse in his ideas, but to say that that puts him on the same level of accountability than Mokyeon is uhhh... Either in bad faith, or delusional, in my opinion.
I truly think both of them are neither saints or evil. Doesn't change the fact that most of the thought processes and choices that led Mokyeon is in his unfortunate suffering hell spiral right now are his own. Nanjo cannot be responsible for how Mokyeon feels, that's a super selfish way of thinking.
Anyway I really like these characters. Would love to have access to the Nanjo cut. Could you imagine a retelling of S1 in his point of view? Hella fascinating
Yeah... I don't think Mokyeon will actually go through with this plan but the fact that he just even thought about doing it and waited for Nanjo at his building several days in a row to do it is... Well, saying is he's unwell would be an understatement. Heartbroken and unstable is a hell of a combination.
But what's even crazier is that Nanjo has almost NO idea about any of that. We as readers know everything about what Mokyeon is thinking, how much he has been musing about "loving" Nanjo, how he tries to rationalize what he's doing, his anxiety, his whole ass tragic backstory... But Nanjo knows none of that lmao. He had a good glimpse of how Mokyeon thinks in chap 34 where Mokyeon cried and confessed to him, but aside from that he has so little to work with ! Like, Nanjo's point of view of Mokyeon must be so insane, if you think about it too hard it almost circles back to being funny.

On a broader perspective, mokyeon definitely is in the wrong. He coerced nanjo into having sex with him...blackmailed him. Sunhwa is no saint, but he's totally unrelated.
Now, on the emotional aspect, yes, I do feel bad for mokyeon. He never had anyone to anchor his love to. The feeling of hopelessness isn't beautiful. Anxiety and bpd is really horrifying and traumatising.
But also, Nanjo doesn't deserve this. U can't force your love on someone. This goes both ways for nanjo and mokyeon. Sunhwa doesn't love Nanjo and nanjo doesn't love mokyeon. That's the truth at the end of the day.
I have seen many people criticise nanjo on insta. But what could be have done. He did the very thing mokyeon is doing- pushing his limits for someone he likes. Not to mention, he was blackmailed and coerced into doing so.
Honestly idk why most people support mokyeon? Yes he's emotionally unstable, yes he has a sad past, but that should not exempt him from what he did to Nanjo.