My Wife’s Next Husband (bottom right image) is the 29th in the Turn Of Fate television short movies and is from 1958.
Ed Barton (James Daly) has a medical examination and discovers he’s got an illness that could take him at any time.
So, in order to get life insurance he approaches a stranger to take the health test for him.
Unfortunately for him, Robert Medhill (David Niven) blackmails him and takes over his life, moving in and planning to marry his wife when he dies.
Barton tried to get Medhill killed but he gets shot himself in the process.
On his deathbed he drifts off, wakes up and realises it’s all a dream.
Medhill is actually the doctor about to examine him for life cover.
Movie pages here.