Shall we be realistic here; well as realistic as possibly in a zombie apocalypse. Nonetheless morals by most would take a flying leap however if the entire world is slowly being overrun with zombies (ala Resident Evil, Dawn of the Dead and etc) really what is the point in surviving? Odds are rather certain you will be screwed eventually unless you are strong enough to challenge an entire population of mutated corpses.
Humane thing to do would be a double murder suicide because the alternative will be immensely more painful. Granted if pain is your pleasure then by all means, be devoured.