Periwinkle dresses and Third-wheeling

Harry Potter fanfic about Dreur (Draco Malfoy and Fleur Delacour)

When Hogwarts hosts the Triwizard Tournament, Draco finds himself falling for the beautiful, charming Fleur. Things between them grow complicated as Draco is pressured by his family to become something he isn't...

(Although this fanfic is set in 4th year when there was the Triwizard Tournament, the Hogwarts students are basically two years older)