Selena Gomez -- Why So Glum? [PHOTO]

A somber-looking Selena Gomez caught a flight out of LAX yesterday ... one day after news broke she and Justin Bieber called it quits.

The couple split after nearly two years together. Various reports say Selena's the one who put the pin in the relationship.

The couple has dodged break up rumors several times, but the handwriting was on the wall when Justin was seen taking in a Broadway play with Victoria's Secret model Barbara Palvin.