You’re kind of right but I think you got the roles reversed the guy with the white hair in the past was kind and in love with MC but his half brother the guy with black hair in the past was obsessed with MC and even forced him to marry him leaving the white haired guy just to watch on the sidelines and so after they both died white hair guy possessed black hair guy’s reincarnated self when he was hit by the trunk now so he can be with ML without the obsessed with black haired guy being there. This is even shown with the black haired guys eyes and hair changing to what the white haired guy used to look like in the past
So your hypothesis is that black hair is faking been white hair so when white hair comes back (I'd he dose) kwon would still stay with black hair.
This is actually pretty solid
Oh I think I got the plot now. ML is actually the bad guy and he was the one killing everyone around MC and the reason why he couldn't get near anyone in this life is because ML would hurt anyone because he is way to obsessed with MC and the black hair guy was actually his true love