In Left 4 Dead 2, if you leave the safehouse to defib a Survivor, in a Versus round, you earn the "Heartwarmer" achievement.
"Y'know all those things I said about you Ellis? I was joking..."
Doubles as a Tearjerker, since Nick will only say this when Ellis has died.
These lines in Dark Carnival where Nick enters Sincerity Mode towards Coach.
Coach: Once the world goes back to normal, I'm buying you guys a steak dinner.
Nick: Buddy, you get me out of this alive and I will deep-fry you an entire goddamn cow.
In one campaign, you come across a bride and her wedding communion, which despite all of them becoming infected, they faithfully sit in their seats and wait for the groom. Even the bride, who has become a witch, sits there and waits patiently for him.
To hammer it in even further, despite her having the usual witch temperament, changing the music on the radio will make her go utterlybonkers on the guy who did it, showing that despite her infected state, she still cares about the wedding even if it's all but dead.
In the trailer, Coach is knocked backwards by an explosion and Nick immediately rushes in to help him back up.