Normal Adolescent Behavior (movie, 2007)

High school student Wendy has an odd relationship with her five friends: They're openly sexual with each other, swapping partners every week. But this is all thrown into turmoil when she meets Sean, a new student in school who has a crush on her. Wendy wants to be with Sean, but doesn't want to disappoint her friends, whom she has known since grade school. When she does decide to leave them, her best friend, Billie, threatens revenge.