I understand ur point, but also, some people do genuinely change. We've seen him, but this is ONLY through Huijin's perspective (right??), and huijin's perspective of him is extremely biased. Huijin viewed seonwu with jealousy/possessiveness bc he thought/hoped that seonwu needed him as much as he relied on seonwu. Maybe in our eyes /seonwu's perspective, he seems like a social butterfly, but what if that idea was just exaggerated? Regardless of that, it's clear that he was also not making direct advances toward jae-eun...... he helped her first, but also that's his job as a person working in a library. Furthermore, again, he is an architecture engineer with clear knowledge about "nerdy" topics.
also ik some things are implied like omg he's so good in bed so that must mean he sleeps around, but also, our mc is inexperienced too.
overall i do agree that lying isn't a good foundation for a relationship, but so many people change themselves to appeal to their ideal. I don't think it's necessary horrible as long as it's not harmful.
I think his nerdy charactor he is playing (if he is, author is doing a good job kepping foreshadowing low key) is tequired not to make a move cos genrally nerds dont (and mc clearly like shy/cute types). But all the patterns are there if you know where to look. Smoke and fire and all that stuff. Could be wrong and its a misditect for some ttauma stuff but genrally authors make it more obiouse when its misdirects. Idk ╮( ̄▽ ̄)╭

why are we calling Seonwu a fake nerd when bro is quite literally talking about string theory and actual topics in advanced physics... He might just be more emotionally aware but that doesnt mean he's manipulative (in a harmful way). Like we know HuiJin is jealous and wants Jae-eun, is it bad of seonwu to be possessive of his gf??? like