I’ll start with one of the most obvious: The death of Henry Blake on MAS*H.
And here are two more:
A Twilight zone ep. from the 1980s incarnation called “The cold equations,” in which a man on a small space shuttle must jettison a female stowaway in order to save his own life–and I believe something else was also at stake here that was much bigger, though I can’t recall what it was. The ep. ends with the man crying his eyes out since he had no other choice than to do what he did. The network had fought this ending, but the producers won out.
And another TZ ep. from the same decade, called “The Toys of Caliban”:
A retarded young man with a bizarre power to get anything he wants by saying “Bring!” causes so much unintended heartache and trouble that his dad eventually decides to end both their lives by coaxing the boy to “bring” fire and let it engulf their house.