Alright, here's my take:
Yooyeon (white haired, I think that's his name) and Kwon were meant to be together. But Yooyoung (black hair) refused to allow the outcast of their family to have anyone so he took Kwon for himself. Used and abused him. But Yooyeon believed that Kwon actually loved Yooyoung since he never saw the abuse, so a little pissed and sad he cursed Kwon for leaving him. Now that Yooyoung and Kwon were reborn, Kwon remembers his past life as horrible nightmares and his curse hits his family members and he can't love anyone without them getting hurt. Yooyoung on the other hand isn't cursed and gets to live a normal life until he meets Kwon again. Remember, he was about to tell Kwon that he had a dream about him before he got hit. All this time though, Yooyeon was essentially floating around disembodied until he saw the opportunity to take his brother's(?) body, especially because it was close to Kwon. Now, Yooyeon is in a dying body and the only reason he's alive is because of Kwon being near him with his curse and their shared connection. The reason he lied and doesn't tell Kwon who he really is is because he still believes Kwon loves Yooyoung and has been pretending to be him since the accident when he entered the body. Especially since Kwon also believed Yooyoung was a good lover before his last past life dream where he figured out he wasn't. It would explain why Yooyoung(Yooyeon in this case) is incredibly possessive towards Kwon.
The world this has could be interesting... if the mc wasn't a walking fleshlight with no survival instincts despite apparently going through awful shit.. ( ̄△ ̄)
She has 0 character same with everyone else. No one can even relate with her bc shes done to be a airhead just for the sake of being blissfully unaware of her "seductiveness". 100% agree with the walking fleshlight. This is nothing but cheap fap material
I like the world building of witches seemingly being from other worlds and that when someone eats a gem of a witch, they turn into horrific monsters.. but then it's completely thrown to the side for big booba and "oooo, she's naked in public and no one cares!" It's sad. Because I can see the building blocks of a genuinely good world.. but it's just.. nothing. ╥﹏╥