You wind up caring deeply about the affair that began in the 1950s between American teenager Don Bachardy and three-decades-older Christopher Isherwood, the noted British author whose Berlin Stories inspired Cabaret. Isherwood died in 1986, but home movies, photos and interviews evoke his presence. And Bachardy — now a famed portrait artist speaking from the same Santa Monica home where he lived with Chris in defiance of the closeted times — shares intimate details that bring the relationship and an era to vivid life, with glimpses of Tennessee Williams, W.H. Auden and Igor Stravinsky. What could have been sordid emerges instead as fiercely funny and touching. Even the animated sequences featuring the lovers the way they imagined themselves — Chris as a horse, Don as a cat — resonate with feeling and blunt truth.