Past Lives is in theaters June 2. Photo: JJ Geiger/ It was the way people were looking at us.” In a bright corner of Café Mogador in the East Village, the filmmaker Celine Song is remembering the rendezvous at a nearby bar five years ago that inspired her debut film, Past Lives. On paper, the movie is a love triangle formed by Nora (Greta Lee), a Korean Canadian playwright in New York; her childhood sweetheart, Hae Sung (Teo Yoo), who resurfaces in adulthood; and Nora’s husband, Arthur (John Magaro), a Jewish American writer. Nora and Hae Sung knew each other...