He was also neglected and used by his parents since childhood so that's probably where his desperation to hold on to someone he loves comes from because he's never had it before.
he's afraid he'll lose that for sure, and you know how Hyeon-gyeol was worried Yeonjeong was hurt and about to pull away? Like that's a logical reaction to being used and manipulated and lied to, but Yeonjeong didn't because he's used to receiving conditional love
he's used to being used like that, so the hurt about that part didn't even register
instead he blamed himself for something he didn't know, and decided to keep the peace through controlling the narrative by withholding the truth
and you know how in the beginning he said to Hyeon-gyeo there was something important he needed to say??? There's a chance, i'm not sure, but maybe he pieced the pieces together, and figured out the day reseting might have been linked to that shady app, and he was going to confess the truth then, and if so, then we know he's not twisted, but he's behaving irrationally because he got a dose of something that was only in his imagination for so long, and he's scared of going back to reality
yesssss im so excited to see how it all unfolds!!
ITS SO DUMB TO START A RELATIONSHIP ON A LIE, especially if the truth is as harmless as "I did not know"
your man is a pretty reasonable person, i don't think he would have hated you if you'd admitted to it, and helped him out. obviously, i understand there's the fear that if you guys find a solution, he'll want to part ways, but it's also such a dumb idea to start a relationship on a lie.
as Tyrion Lannister says "A day will come when you think yourself safe and happy (in your relationship), and suddenly your joy will turn to ashes in your mouth." inevitably!
as it was built on a lie!
i realize it's a common trope and it's midnight and I'm way too invested
and I also realize that, Yeonjeong is a smart character, and it's not that he made a dumb decision, but a delusional calculated one. It's not that he made a dumb decision, he made one that in foresight he'll see as dumb, but at the moment, it might make sense for his character to try and control the narrative of their relationship
Since Yeonjeong spent so long having a crush and just suddenly had it all fall in his lap, he started slipping into a routine he never questioned, like, this might has well have been a dream for him, it's been too perfect. So, in order to keep the dream-like situation, he refuses to put any type of pressure on it, he'll risk the real and imperfect union he could have for the unblemished perfect narrative of a love life he wants with Hyeon-gyeol, and that's such a toxic behavior, it's a sandcastle, it's a house of cards