Rent Lost and Delirious (2000)

Shy, unassuming teenager Mary 'Mouse' Bedford (Mischa Barton) is enrolled at a prestigious all girls' boarding school. Upon arrival, she is welcomed by her two attractive and sexually adventurous roommates, the carefree Tori (Jessica Pare) and excitable Paulie (Piper Perabo). Mary soon discovers that Tori and Paulie are embroiled in a passionate relationship, yet when Tori's younger sister finds out, and threatens to break the secret to her friends and family, Tori breaks oft the relationship. Unable to deal with losing the other half to her whole, Paulie will do anything to get her ex-girlfriend back, even if it means risking her life...