"Now tell how it is with us."
George went on. "With us it ain't like that. We got a future. We got somebody to talk to that gives a damn about us. We don't have to sit in no bar room...jus' because we got no place else to go. I them other guys get in jail they can rot for all anybody gives a damn. But not us."
Lennie broke in. "But not us! An' why? Because....because I got you to look after me, and you got me to look after you, and that's why."
This is the mantra that George and Lennie recite throughout Steinbeck's Of Mice and Men and it directly concurs with the quote ""True friends depend on each other when they're having a difficult time." In keeping with this, their friendship is a rampart against the terrible aloneness of the other "bindle stiffs," the itinerant workers. Here are some examples actions that accord with this.
When the son of the owner of the ranch enters the bunkhouse and looks threateningly at George in Chapter 2, George knows that Lennie will protect him physically. When Crooks cruelly suggests that George, who has gone into town, may not return and thus leave Lennie on his own, Lennie insists,
"He won't do it..... George woudn't do nothing like that. I been with George a long time."
When Crooks continues to banter with Lennie, Lennie finally becomes angered, asking, "Who hurt George?" Sensing the danger of Lennie's angry protectiveness of his friend, Crooks gets out of the way, saying that George is all right and will return that night. In response, Lennie loyally growls, "Ain't nobody going; to talk no hurt to George."
Of course, in the final chapter, the loyalty and love of George for Lennie is certainly demonstrated. For, after Lennie inadvertently kills Curley's wife, he runs to the planned spot for sanctuary and awaits George. Sadly, George realizes that Lennie will be put in the "booby hatch," as Crooks has said or executed; unable to stand the thought of Lennie living caged like an animal, out of love for his friend, George shoots Lennie in a mercy killing.