You were suddenly reincarnated as a side character, luckily a noble to a novel you were reading when you were back in earth. 

It was a fantasy, romance and historical novel. Just like any stories, they have Female leads and Male leads but you become the side character of the story instead... 

And ended up with the villain of the story. 

You stole his first night... As he also stole your first night. 

They all don't know that this is a novel, since they're just characters