Anyone who mattered knew the truth. That was enough for him. Hermione had insisted on keeping their relationship a secret until after N.E.W.T.S so their studies wouldn't be distracted by the attention from the school and the media. Draco was the heir to the Malfoy fortune and Hermione was already making a name for herself as the brightest mind in their generation. They were subject of articles separately as it was; if they were to go public, the story would be everywhere for months. 