ALFRED HITCHCOCK PRESENTS (1987) - Deathmate

The story is about a wife who has an affair with a younger man. She wants to leave her old rich husband and runs away with the young man. But the man has another thought. He wants to be with her because of the money. In fact the man has lover already. So if she runs away with him without inheriting her husband wealth, his effort will be useless. Eventually the young man kills her husband and makes it as if the man drowns during his bath. Suddenly she appears and thanks to him by pointing a gun at him. She said "I better be a rich widow than a runaway wife" :D