hmmm i think that's kind of wrong though cause isn't just that the villains are not whom you thought they were instead of being Eugene the villains are the woman from the geld family or whomever separated them?
Yeah. They're the villains. But the woman only stated that he was going to marry the ML and flashed some ring (Of course she would. That was his family's plan and the marriage was prob arranged. And the FL was a commoner.). The FL immediately despaired without confronting him and then died from fever, probably due to stress. Centuries passed but the (unjustified) grudge and regrets remained.
True, it's kind of ridiculous and it makes the FL look like a really weak character, though it did state that this was after she tried to talk to him for a while and they refused her, though knowing he refused to marry makes that make more sense, makes that 500 yr grudge look stupid too.
I hate settings like this where the story makes you think frustration you felt through the lead wasn't worth crap because it really was just a misunderstanding on the lead's part. So you're left with nowhere to vent it out because even the villains didn't make any gut-wrenching foul play to tear the lovers apart.