During the 1930s, there were thousands of white American men who were displaced as they had to give up their homes in search of work. Alienated from one another, in this isolation of itinerant worker, few became friends with others. As a result, there was a tension among workers, for they did not have the bond of trust.
But George and Lennie are friends. While George complains, saying in the first chapter,
"I could get along so easy and so nice if I didn't have you on my tail. I could live so easy and maybe have a girl....You can't keep a job and you lose me ever' job I get...You keep me in hot water all the time."
Angered with Lennie for keeping a mouse in his pocket, and for forcing them to leave jobs, George continues to relate the sacrifices he has made,
"When I think of the swell time I could have without you, I go nuts. I never get no peace."
However, when the hurt Lennie says that he can get along with George, George softens and tells him that he wants Lennie to stay with him. For Lennie, George recites their mantra of the dream of owning their own place,
"With us it ain't like that. We got a future. We got somebody to talk to that gives a damn about us."
Then, in Chapter Two, George explains to the boss who comments,
"Well, I never seen one guy take so much trouble for another guy. I just like to know what your interest is."
George lies on Lennie's behalf,
"He's my...cousin. I told his old lady I'd take care of him.He got kicked in the head by a horse when he was a kid...."
When the other bindle-stiffs say that they are going to town to gamble and get some girls, out of friendship to Lennie, George replies to Whit,
"Me an' Lennie's rollin' up a stake,...Imight go an' set a and have a shot, but I ain't puttin' out no two and a half."
In the final chapter after Lennie tragically kills another woman, he runs to the clearing where they first camped before coming to the ranch. When George arrives, Lennie asks him, "Ain't you gonna give me hell?" but George does not, out of his love for Lennie. Lennie offers to go away, but George tells him "I want you to stay." George, then, sacrifices his job, his new friendships, and his own comfort for the sake of Lennie, whom the others will harm if they catch him. With one shot to the back of his head, George sends Lennie to a place where no one will harm him.
"No, Lennie. Look down there acrost the river, like you can almost see the place....."
Go on, George. When we gonna do it?"
"Gonna do it soon.....Sure, right now. I gotta. We gotta."
In the novella Of Mice and Men, written by Steinbeck contains many sacrifices that friends make for one another. For quotes you are on your own - I will just provide you with the places to look for them.
One sacrifice is George gives-up his freedom to look after lennie as Lennie is facinated by soft things and soft animals, which ultimately cause conflicts leading to situations for George to rescue Lennie.
Lennie sacrifices his strength for George so that they may obtain labor doing field work - Lennie strength is that of two men that enables them to find work and be hired when there is work available during the Great Depression.
The ultimate sacrifice is after Lennie is attracted to what a flirtatious female is called a vamp. She is attractive to Lennie because she looks soft to him and he yearns to pet her. Alone in the barn she flirts with Lennie and lets him pet the back of her neck. When she realizes the strength of Lennie's touch she panics and starts to scream. Lennie panics because he does not want to be scolded by George and in an attempt to quieten her he breaks her neck. He flees knowing that what he did will make George so mad that he will take Lennie's dream away from him - that which is raising all of the rabbits he wants. George finds Lennie in a designated spot - he begins to calm Lennie by telling him the story that he longs to hear about the land and rabbits that they are working to buy. George motions to a spot behind Lennie - as Lennie turns he shoots him in the back of the head to save him from the torture that he would receive from the husband of the women he killed.