
Nah I won't lie, I'm fine with the side stories.

Welllll
It's their past lives, I doubt she remembers the atrocities she did during that time as it's not specifically stated that she planned and manipulated everything in the main story because she remembers. In a sense, the implication of the ending is that, they are always fated to meet each other in whatever lives they're in. It's just that, Sia's soul strives to choose an identity that distances herself from Heeyoung (as to not hurt him).
I freaking hate it when stories use 2nd mls.
For God's sake, why bother adding 2nd mls if the story is gonna end up with them fl and ml together in the first place. Y'all are treating 2nd mls like used condoms to be thrown away after use.