“Marianne & Leonard: Words of Love,” is about the enduring love between the Canadian singer-songwriter and poet Leonard Cohen and Marianne Ihlen, the Norwegian woman he met on the Greek island of Hydra in the early 1960s. It’s a story that is at once simple and threaded with startling complexities. Its emotional entanglements and narrative twists can seem the stuff of fiction. They shed sometimes discomfiting light on the expansions and excesses of the 1960s and ’70s counterculture that its main players helped to define.