Shiroki Otome no Werewolf

Hakurai Private Academy, a boarding school where young ladies receive a higher education in bridehood. Should the maidens lose their "purity" during the three year course, they are immediately expelled, losing any chance at their dreams of becoming brides. For the girls living at this school, it is a future they consider worse than death. One day, something happens in the dormitory of the student council! In their midst is a two-faced wolf aiming for their purity, and it is up to them to pull back the mask!

(Source: Takeshobo, translated)