Astronauts Suffer Tragedy and Betrayal Midway Through perilous Space Mission

Two astronauts are on a six-year mission when disaster strikes, leaving one astronaut's family murdered.
The surviving astronaut allows his robot doppelgänger to comfort his mourning colleague, who becomes obsessed with the astronaut's wife.
The obsessed astronaut eventually murders his colleague's wife and son, leaving the astronauts stuck together in space, one a murderer and one falsely accused.
The episode follows three people in an impossible situation leading to a tragic end and is driven more by empathy than metaphor.
The story is set in an alternate 1969 and focuses on the grounded performances of the actors over clearly metaphorical themes found in other Black Mirror episodes.