A friend is someone who turn around and see if you are still around.
A friend is someone that go back to help you when you aren't.
A friend is someone who keep playing with you even though you keep making mistakes.
A friend is someone who doesn't fire back when you accidentily shoot them.
A friend is someone who never take your medkit without asking, and always share their own when you need it better.
Luckily for me I have a whole bunch of very good friends to play L4D2 with. That's what keeps me coming back over and over, and I won't stop before I am dead for real.