Takashi's words as he embraces Rei in the first episode. It's both heartwarming and tearjerking.
Takashi: On the day everything came to an end, I killed my best friend, then I held the girl that I loved... for the first time in my life.
One of the more disheartening examples occurs during the third episode, when Takashi and the others are escaping from the school with another group of survivors. One of the other group's survivors, Takuzo, is overwhelmed and soon mobbed by "them". When his girlfriend, Naomi, sees this, she rushes back to his side and certain death, without a moment's hesitation. Saya tries to tell her that it's too late to save him:
Saya: Wait a minute! You heard me, didn't you? He's not gonna make it! Why are you going back to him?! Shizuka: [solemnly] I understand. If the entire world turned into this, I'd rather die with the person that I loved.
Kohta giving Saya his MP5 and taking her pistol when she was complaining about feeling useless. This wouldn't be a huge deal most of the time, but for a gun otaku like Kohta it means a lot. The others who saw it treat them like they got caught making out.
A slightly morbid example from the third extra chapter has the undead Morita approaching the undead Misuzu (the BFF with Odango Hair). At least in death he finally got the girl....