Lost and Delirious (2001) on Netflix

When her father re-marries after the death of her mother, Mary Bedford finds herself bundled off to a posh girls boarding school. She's never been to boarding school before and it's all quite daunting at first. Soon however she makes friends, including her two roommates, Tori and Paulie, whom she soon realizes are lovers. She also becomes quite friendly with the gardener, Joe Menzies, and helps him on the school grounds as it reminds her of working with her late mother in the family garden. When Tori decides to end her relationship with Paulie however, tragedy ensues.