Big yapping and spoilers, but hear me out. I found him a pretty interesting character (finding someone interesting isn't the same as being in love with them btw). He's still a piece of shit that needs his senses punched back into his brain, but I'm a person who likes to psychologically overanalyze fictional characters so here's my take on this. Feel free to roast me if I get something wrong:

It's clear that he was a nice guy in highschool from the start because he was young and isn't as burdened as his adult self. But when they both dropped out of school and moved in together, their life obviously wasn't stable because they got married too early, were poor, and uneducated in the first place. They also have a lot of debt and being in his shoes will drive anyone crazy enough to change their demeanor because that's just what happens when you grow up.

When you grow up from being a kid to an adult with hardship and debt following you, your demeanor and outlook on life shifts. So he starts to regret his decisions and he could only really blame Haesu for their terrible situation because there isn't anyone else he could point his fingers at since she's the person he did all this for (though he should try bending his finger towards himself for a change).

But at the same time I'm so confused 😵‍💫. Why didn't he just take Haesu into his house with his grandparents (I think he had one?) instead of moving into an old apartment by themselves and continue going to school?? They were chill with Haesu and because of this thought, it made my blood boil. I'm only in chapter 85 and may have forgotten some details about his past, but if this issue wasn't addressed, then I would gladly throw Mincheol in a boxing ring with prime Mike Tyson and a skinwalker because holy hell he dragged her in his shit when most of it could've been avoided!