
From what I understand, he treated Na Haeso badly because she's a reflection of his incompetence -- like those shabby clothes she wore, or how she is working so hard. He made those promises when he was young, but not one of them came true; worse, they are in debt. He cheated because he needed an ego boost and an escape from reality.

Oh my god!! That's very true, it was mentioned about how he felt about her shabby clothes. It's honestly sad, he's the reason why they are in debt, instead of pushing through he decided to become bitter and not even try to make their life better. So Na Haeso had to bear all of their problems and work multiple jobs. I understand if he felt less of a man but he could have tried to help instead of being a turd & cheat & knock her down. Honestly I like how he is written, it shows how some people can become(in real life)
It amuses me how people don't know how to appreciate really well-developed stories. I've never seen such a deep dive into male psychology as in this story.
And I really like that Mincheol is not a cardboard villain with only one characteristic, but a multifaceted figure, a well-developed character.
In this story, all the characters are "in 3D", living, real people. Each one is crippled by life in their own way. And it's fucking awesome to read stories where people look like real people.
So all these whiners in the comments really piss me off.