ONCE UPON A TIME - "The Shepherd" - David must choose between staying with Kathryn or leaving her to be with Mary Margaret, with whom he's fallen deeply, and inexplicably, in love; and Emma catches Sheriff Graham in a lie. Meanwhile, back in the fairytale world that was, Prince Charming is about to encounter a life-changing event that will forever alter his destiny, on "Once Upon a Time," on "Once Upon a Time," SUNDAY, DECEMBER 4 (8:00-9:00 p.m., ET) on the ABC Television Network. (ABC/JACK ROWAND) ROBERT MAILLET, JOSH DALLAS