I mean it seems like the Duke joined the original Villainess' side in the 2nd timeline (the one where the original book's plot took place since it's the REVENGE part), so they weren't probably on great terms from the start. That's what it looks like in the webtoon when the MC is thinking about the og story, anyway. BTW, it really doesn't make any sense that the MC doesn't know the Villainess' "truth" aka her true origin that was revealed before her death & thus would have been the first thing mentioned in the book's prologue or even in the summary as a hook for the reader (cuz you KNOW that the antagonists would have taunted the villainess with it right before she died) & also would have been a huge part of her revenge & something the Villainess would have been obsessed with for most of the story. That's like remembering all of Harry Potter but not knowing that Harry is the Boy Who Lived & how there's a big prophecy around him killing Voldemort but for some reason you DID remember that "oh yeah, Voldemort killed Harry's parents! Not sure why tho, probably not important~". Author, what the heck???