Night Trip (1982)

12-year-old Thomas takes rowing lessons and grows rather fond of his teacher. He idolizes his trainer – and when the boy discovers that the person he felt such a love for lied to him in order to sleep with his mother – his heart is broken. It's hard for him to understand why his trainer would prefer to be intimate with his mother than to be with him.

Unfortunately the movie Night Trip is not yet available on HBO Max.