Draco and Florence are both Pureblood Slytherins. While this may hint at an alliance, they've hated each other since birth, when their parents, both sets Death Eaters, forced them together for a chance at another line of purebloods. When both fifth years are picked as the prefects for the Green Hogwarts house, they're forced to spend time together. Once arguments are fought and feelings intensify, The Dark Lord returns for good, forcing Florence and Draco into servitude because of their parents' sins. This turn of events brings the two physically closer from family ties, but spiritually farther apart from different moral standings.