It's a thin line between love and friendship.

Something Borrowed (2011)

Though Rachel is a successful attorney and a loyal, generous friend, she is still single. After one drink too many at her 30th-birthday celebration, Rachel unexpectedly falls into bed with her longtime crush, Dex -- who happens to be engaged to her best friend, Darcy. Ramifications of the liaison threaten to destroy the women's lifelong friendship, while Ethan, Rachel's confidant, harbors a potentially explosive secret of his own.