Bri

Yuri is not his cousin but his brother, other than that I agree with everything you said!

Seojin is a massive hypocrite who demands from Yoonhee stability and confirmation of love when he won’t give it and gets pissy when Yoonhee doesn’t give it back either. It isn’t just him seeking physical affection, he takes advantage of feeling special because Yoonhee makes him feel that way, he enjoys being Yoonhee’s first, of possibly being the only one Yoonhee, a person who is going to have a lot of power and currently has a lot of power, love him. He likes keeping him on the hook on his terms and doesn’t want to give any assurance back. He isn’t “only thinking by his dick.” He is being fulfilled emotionally by Yoonhee and will not reciprocate. Yoonhee is younger and has been brainwashed to be a snake god’s companion since he was young and whatever Seojin has seen till now of Yoonhee and Yuri is that Yuri is basically his servant who is abused (Yuri being younger than both of them) and every action of his points to him being an expendable servant so Seojin being “jealous” ( because he IS jealous more than he thinks it’s weird) makes him a massive douche because why isn’t he more worried for Yoonhee???? Or even Yuri for that matter??????

Yep, he is a douche and since the beginning of the story we know he has never been able to have a normal relationship because he doesn't reciprocate in a normal healthy way. He is a dysfunctional character, result of his trauma. Yonhee and Yuri also have trauma but since their grooming is a more systematic one, built through generations of their family religious bussiness, they've come to terms with who they are supposed to be. Yonhee and Yuri have survived because they fulfill their roles and there is no conflict (until now) about who they are. I'm not saying they don't suffer, but it makes their actions and decisions very clear, very goal oriented, because they have a purpose. They aren't actively traumatized, because their system is 'functional', but they lack so much of the normal human relationships so of course Yonhee is hungry for affection, and Yuri only knows how to be in relation to his usefulness to Yonhee. This makes for a dynamic in which they will always be pulling.
Seojin wasn't groomed like Yonhee or Yuri, but his parents got him to be an accomplice in the factory murder and then to starve his brother, the root of the problem. He then roamed the streets with Seoyeon on his back. That's why He loves him but hates him, he takes care of him but wants him death. It's ironic that the only "stable" and long relationship he has is with said brother. Seojin has a major conflict with who he is and what his "role" is supposed to be, only drifting through life and thinking about his survival. Ambivalence never leaves him and i reckon this fucks a lot with his relationships. So this makes for a dynamic in which he will always be pushing.
This relationship is complicated and hits right in each of the characters conflicts.
Yonhee has no issue with sacrifice or devotion because he comes from a place where those are rewarded values, while with Seojin is the complete opposite, he rejects that attitude.
It's sad because Yonhee is compromising his own wellbeing for being with Seojin but the other doesn't see it. He is more concerned about his own safety and he projects his internal fears onto Yonhee.
He's definitely not a saint, no one in this story is. They're also not demons. They're human. They want things that they shouldn't want and they suffer in the process.

This story focuses on the relationship between these two, so of course that's the angle we're going to take, and we're going to judge how these two go on about each other, but this doesn't happen in a vacuum. I just think this plot goes beyond characters being "massive hypocrites" or "cunning" (i very unfairly called Yuri like that in another comment) as they're more complex that that.

Completely agree with you! I feel as if some people might be too harsh on just seojin. I can see why he may be frustrating as a character, but considering his upbringing it’s understandable why he acts the way he does. I found it interesting how much more criticism seojin seemed to receive as none of the characters are saints like you said. This story is so complex and captivating, and I can’t wait for more to be revealed and developed between the characters.

lmfao u sound like u want seojin to carry the burden of all the problems in their relationship. why is the burden to be mature heavier on seojin's side when yoonhee has a lot of growing up to do as well? is it just because seojin's older by two years? but considering the power dynamics between the two, as u urself had mentioned, in a way yoonhee has more power over seojin isnt it? he could fuck him over in the blink of an eye. and as other replies had pointed out, seojin had always been in a constant state of survival ever since he was young and he had no control over his life and decisions, like ever. someone like that is bound to be guarded, and his first instinct in any situation is to protect himself from being hurt and taken advangtage of. of course he's afraid to fully commit because there are a lof of things he doesnt understand about yoonhee, this has always been explicitly mentioned by seojin himself all throughout the story. and it's very clear that devotion to yoonhee requires devotion to his clan as well, that factor alone triggers all of seojin's trauma lmfao you;re making it sound like his actions were all calculated but he's actually just a teenager who is not mature enough yet to act based on logic all the time, he had even questioned himself multiple times because of how drawn he is to yoonhee despite wanting to distance himself from the "weirdness" of yoonhee and his clan. yeah seojin is a hypocrite, and a massive dick, but what ticks me off is how much context is lost just because u hate his character and prefer others much more.

and omygod sorry that seojin had no time to care about the well-being of someone who clearly dislikes him (yes, im referring to yuri) lmfao i mean i feel bad for yuri too but why do u want seojin to act like a fully matured individual. ur clearly missing the point of his character sjfhksjfl