This is based on opinion. Please don't list it on a work's trope example list.
Tearjerker / The Last Man on Earth
From the movie:
Morgan is forced to kill the dog he managed to befriend because it's infected.
Morgan discovering in the end that all his efforts to find a cure and end the undead menace were worse than useless.
Morgan trying to get the soldiers at the pit to give him back his daughter's body, only for a military policeman to tell him that there are lots of daughters down there, including his own. Her body is tossed into the pit, and for one long moment Morgan is clearly willing to jump after her.
From the TV series:
"No Bull": Phil insisting to Phil #2 that they're family. Probably because he misses his brother, who's really still alive in space.
"Silent Night": Phil #2 is stricken with appendicitis. Gail and Todd attempt to perform the surgery, but Phil #2 bleeds out. Gail and Todd try to staunch the bleeding but in the panic of the moment, the monitor flatlines. The next episode reveals that he died on the operating table.
"Smart and Stupid": Todd started yelling at Tandy for spending time with his brother, until seeing Mike cough up blood, a symptom of the virus. Tandy keeps on insisting that Mike just has a cold, but the rest don't buy it after the calf's mother dies from the virus. The next episode continues on this, with Mike accepting the fact that he will die and realizing his brother buried his family after the virus.