George does act like a protective older brother to Lennie, and Lennie looks up to George. George looks out for Lennie, telling him how to behave and what to do and what not to do. He also encourages him by telling him they will one day have a ranch where they can tend rabbits.
Lennie often asks George if he is mad. He wants to please George, even though he sometimes can't control himself.
"I ain't mad at you. I'm mad at this here Curley bastard. I hoped we was gonna get a little stake together- maybe a hundred dollars." His tone grew decisive. "You keep away from Curley, Lennie." (ch 2)
George is constantly worrying about Lennie. He is afraid that he will do something or say something to get them kicked out of work or run out of town, such as when Lennie wanted to touch a girl’s dress. Of course, George’s fears are well-founded. In the end, he cannot protect Lennie from others and he cannot protect others from Lennie, so he shoots him.