I love this analysis so much and it's spot on with everything we've been showed in the story so far. I normally find push and pull dynamics and misunderstanding tropes annoying. But with the way the story was told and the way the background was expanded on I'm more sympathic to the characters than annoyed. The reread hits different with the full context of their past now revealed.
While I hate Jaewon with all my guts I also sort of sympathize with him as well. Although he was less fleshed out compared to the main couple there's still suble character building at play for him. The reason he lashes out the way he does is because he resents the fact that Seo-in was brought in as his replacement. He's been sickly from a young age and his parents (especially his mom) are torn up about it. No matter how much they claim they love him they love the idea of a "perfect" family much more. Having a sickly child gets in the way of that, so imagine how Jaewon must’ve felt when his parents suddenly bring home a new model so to speak. One that not only looks just like him but doesn't have any "defects" either. A perfect replacement. While that in no way excuses his actions it does explain why he acts the way he does.
Overall I really love the characters and story telling. Each new chapter is the highlight of my week.
What bugs me is 10 years time skip, 10 years isn't a short time
So from my understanding, Seo-In has an obsessive personality type but is afraid to reach out first because as a child, he's felt that rejection of love from his adoptive parents. As a result, he tends to probe and prod at others to essentially test and push their affection. We saw that with the couple as children, and it also explains why he's so push and pull with Yeongwoon. He tends to be sweet when the MC is, but retaliates at any slight hint of Yeongwoon pulling away.
Yeonwoon is also seen to be a little possessive of the ML(although within very reasonable bounds) but because he feels that he's been played with and used by Seo-In in the past as a stand-in(at least in his mind), now he's particularly wary of getting too emotionally invested. So he tends to push and pull too, but bc he's got this whole inner conflict going on.
Jaewon is my least fav just bc he feels very one-dimensional. He repeats the same lines over and over again, 'youre my shadow'. If we at least saw signs of him being upset by their parents attention to Seo-In, or that he was greedy for his family's attention, id understand him more. I wonder if the author will flesh out more about how his illness impacted his mental health bc most times we see him, the dude seems fine. But someone once said he's not a real antagonist, but rather a plot device, which i think makes his repetitive character traits more bearable.
The mom is interesting. She definitely cares for Seo-In, but I think she just prioritizes the idea of her perfect, unbroken family more. She might actually be more biased towards Seo-In as the stand-in for her dead son and the one that followed in her footsteps than Jaewon.