The beginning of a nightmare

The past...such a beautiful thing. Until it comes back to haunt you, but when the real question arises nothing but fear trembles through your body. Where did he come from? And why does he know so much about her? But is he really there for her? Or to help them not make the same mistake? But in the end of the story, what's the outcome, does a cursed past repeat, or is it intervened by magical beings that should not still be there.