beta
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.