Nighty Night (2004)

Season 1: Episode 6

Don and Cathy split up. Jill kills Terry, then forces Glenn to kill Gordon the vicar with a poisoned sundae and makes him confess to the police. Then she tells them him they can start a new life- well death together. He eats one of the other poisoned desserts, then gives it to her, saying it's her turn. She tells him she's not really hungry and watches him die. Terry turns out to be alive after all.