Sorry... but...

It’s hard to explain and it would probably be explained more in later chapters but basically what I’m getting at is the black haired version of yooyeon is the real one. The black haired yooyeon was manipulative, evil, and abused kwon in the relationship in the [past life]. Once the white haired yooyeon (good yooyeon) found out about this he couldn’t stand it. Which makes him form an unhealthy obsession over kwon but they eventually they all died since it was the past(white haired boy has unrequited feelings for kwon in the past). So in the [present life] as you can see the black haired yooyeon (the abusive one) was reborn and became friends with kwon but Kwons “curse” gets him hit by a truck. In that moment the black hair yooyeon “dies” and the white haired yooyeon takes over that body. The reason the white haired yooyeon takes over that body is because he is extremely obsessed with Kwon and wants kwon to fall in love with him. Which is why you can physically see in the present day after the accident yooyeons present form switching from black hair to white hair. So basically the white haired yooyeon is a curse formed out of obsession and unrequited love in their past life which is what is causing kwon’s “curse”. The white haired yooyeon was not supposed to interfere with kwons present life but due to his obsession he takes over the black haired yooyeons body so he can stay with kwon forever even if it hurts kwon. [Think about it this way yooyeon in present day originally had black hair but after the accident it changed to white which means the black haired yooyeon is the original and the white haired yooyeon is fake and not supposed to be in that body meaning he is a curse]. Sorry if it’s long it’s really hard to explain this !!

So they are basically both evil

Wow that explains a lot. Thank you so much, because I skip many chapters to avoid the smut part (bcs it's too much for me) so I lost track ini the story.

So basically, there is two yooyeon from the start (past life)? And the reasons still unknown? Or they're twins? The father of white yooyeon seems to despise him so much.

Of course no problem! I think that part might be explained I tried to look it up and it seems like the two yooyeons are two different people. The white haired yooyeon in the past life was hated probably due to his light features. As we see many times in past life scenes albino people (people with very light features who are typically born from people with very dark features ) were seen as demons and curses. Because during that time no one knew it was just a simple skin condition and a lot of times in these scenarios the mother dies(for some reason I don’t know about that part). Which is probably why the father hated the white haired yooyeon.

So I’m guessing the white and black haired yooyeons are two different people but the white haired yooyeon purposely turns into a curse so he can be with kwon in the [present life]!