Focusing on the wrong things?

Literally this

But the author is doing exactly that. Why do you think Jihyuk jumped to another relationship right away? Even if he doesn't have as strong feelings for Eunsong he wanted to feel chosen and someone to fight for him since his parents death.

This clearly is not the right way to deal with his issues but that's what I like about this author. This is the story of broken people dealing with trauma and how even if you're a victim, you can damage other with your actions. Jihyuk feels he doesn't deserve to be loved even if he desperately needs it, Eunsong because of society expectations has to be ruthless if he wants something even if he hurts the ones he loves through his means, Yoojun never knew what it meant to be loved so when he experienced just one (1) positive relationship (Eunsong) he disregarded everything even his own feelings. You can even talk about Jihyuks brother and how his own feelings of helplessness destroyed his relationship with his brother even if he tries to fix things.

I think that the path of Jihyuk choosing himself would be the best, but, do we humans always choose what's the best for us? Or what's the less painful thing?

I like your analysis but in order for me to be fully content with it, I NEED the ending to point towards Jihyuk choosing himself. So many stories though have the ending where the main character chooses to stay with love interest because they feel more comfort despite their wrongdoings, and while I do think it can still work as an ending, I feel like for this story it would turn out more sugarcoated rather than obviously psychological (and I really don’t think the author is going for this dark angle lol)

An ending where Jihyuk chooses himself would be so perfect because you generally don’t see that in “romance” stories. It’s the best, meaningful ending, but not for a couple, but for Jihyuk.