idk the story is a bit confusing.
since it was going so fast i really though she was doing to die and reincarnate somewhere else with the demon king or something. for a moment i was really expecting another timeline change.
i really don't know what is what, but i can guess
tbf, my theory, by now is that the hero is the 'evil' (from her perspective, not evil evil but simple her enemy), she loves the demon king (her origin is that side) and is probably also a source of power (some couple power, love win lul). so the whole plot is she was cursed (kidnapping over reincarnations) and the hero job is to make sure the girl is far away from the 'demon king'. the demon king is probably not that bad, only someone strong that was called a villain by the hero side, maybe from earth too, or maybe he helped mc when she came from earth.
the whole curse on her is to weaken the demon king, they never kill him, since there is always 'another king' to be defeated. but by keeping her 'away' they can get the upper hand. him never coming back (past lives) is probably because they succeed on sealing the demon king temporally, but every time she revives the seal is broken (but because of the curse the hero will always be there to use magic on her making she forget her past).
the last time the demon king failed, maybe it is a distance thing or maybe her love makes the hero stronger, but now because she moved and begun to seriously move on from the guy, something may have changed and the hero is back to make sure she still loves him. trying to weaken her connection with his enemy. i would bet he has been using love magic too and he may be even the same person or they all received the same mission, or why would she still love the hero even after being traumatized? i would bet she would be wanting to not even be friends with a hero, the same reaction she has for other potential love interest or even worst. but she is always falling in love only with the heroes, and that is too suspicious!
i wonder tho how dramatic will it be, i am sure things arean't as it seems, it only depends on how sickening the author will make this be, how manipulative or how cursed is her existence and why thing are what they are for now.