So i just finished the game and thought i was amazing.  However i have a couple questions about the ending. 
1. Is the phrase at the end meaningful in the book or did i just miss something? 
2.  I wasnt able to tell who gave me the revolver at a glance so who was it?

It was probably a reference to something in the book. I don't think it had been mentioned in the game prior to that. 
 
My interpretation of the quote, is that it was more of question to you for your final choice in the game. If you get the option for both endings, you basically decide the fate of the dark ones, so you have to determine whether or not the dark ones are indeed hostile, and whether or not you should kill them. 
 
I couldn't tell who the guy was either, but he could have just been some random dude embodying the somewhat ignorant idea that you can solve the world's problems with more violence, or, like I said above, he could just be any random dude to serve the purpose of posing that question to you. However, I'd assume it's the guy who was attacked by the flying demon near the top of the tower. I can't remember his name, and I could hardly tell them apart due to the helmets the guys were always wearing, and the very similar character design.

I think Miller said that at some point.  Maybe before you left Polis?  I think it's the Ranger motto.
 
Here's the guy that gives you the gun.  He's not familiar to me. 
 

So is Hunter the man who gives you the gun?  They look similar:
 

It's Hunter.