Widow Blue! (1970)

The main plot line of Sex Psycho AKA Widow Blue. revolves around a debased couple who are cheating on each other. Jerry is cheating on his wife with a woman named Eva. Jerry plots with Eva to kill her husband. They do this by luring him in with Eva's handsome brother and brutally killing them both while they are having sex with each other. From this point on, several twisted scenes are enacted, including fellatio on the dead husband, incest in a coffin, and a gruesome castration during oral sex. The ending ponders as to whether it was a dream or not, leaving you only to wonder if it was real or imaginary all along.