Okubyouna Hakushaku Reijou wa Momegoto wo Nozomanai

Amelia is an admirer of the Marquise Sophie, content to be an inconspicuous member of Sophie's entourage. One day, Amelia saw Sophie's fiancee, the crown prince, secretly meeting with the Baroness Rosetta. "If I harass Rosetta and force her away from the prince, will that make the prince look at me again?" Sophie asked. No, that will just make Sophie become the villainess! In order to keep her precious Sophie away from the bad ending, Amelia will have to help her with the ways of love! But that draws the attention of Sophie's tsundere brother Rufus...!? (Source: ComicWalker, translated)