You summarized the dark human side of the story so well! But looking at it from a deeper angle, the real tragedy isn't just that Mok doesn't know how to love..it’s that he’s trying to love using the "survival mode" language he learned as a kid. When you grow up with that kind of neglect, your whole idea of giving love becomes total self-sacrifice just to keep the other person around, even at the cost of your own dignity.
On the flip side, Nanjo is a textbook example of using distraction to run away from his feelings. Him clinging to Sunhwa after everything he went through with Mok was never about actual love it was just a "safe space" to avoid facing how complex Mok's feelings were. The story is literally giving us a collision between the trauma of neglect and the trauma of confronting one's own self-beliefs (especially since Nanjo always assumed he was straight).
Mok choosing suicide was the terrifying realization that every single tool he had to love someone was completely broken to begin with :(

Nanjo is not wrong for feeling and acting that way, well he did genuinely like sunhwa at the start so he had to go with mokyeon's blackmail stuff(wasn't actually blackmail but it was close), but ofc sunhwa's a bitch who doesn't genuinely like someone.
Mokyeon's wrong, yes, but I understand his feelings and the way that his backstory(his childhood) affected his present self. I didn't say that it should justified his wrongdoings just because he had a bad childhood, no. He experienced alot of shits that a child, hence a person shouldn't even encounter at all, he suffered, and experienced malnutrition, and the worst of all—didn't experience the love he should've gotten from his family or from someone. Figured that he doesn't know the feeling of love, or the sincerity of it, that's why he sleeps around.
He didn't know how to really express nor know if he's IN LOVE. But, when he met Nanjo? He was clueless on why he was feeling "like that". But too bad, Nanjo's mind too preoccupied with Sunhwa. Mokyeon's confused, he mistook "his" love with "physical connection" and only thought that it's alright that Nanjo like Sunhwa, as long as he's with him. His love is unhealthy, because he didn't know the reality of it. It was basically his first time feeling love, well maybe it's his first time too to experience the pain of "heart"break, since he doesn't really know how to fix it because that pain is different to the pain that he went through before, hence making alcohol and suiciding the only option to remove that pain.