In Of Mice and Men, George is Lennie's friend, his co-worker, his guardian, his conscience, and his surrogate brother/father. More, he is his loving mercy killer. He eases Lennie's pain and suffering after their shared dream has gone awry. In short, George loves Lennie on more than one level.
Unlike the other migrant workers who travel alone and view the world as a "me" versus society ("Guys like us, that work on ranches, are the loneliest guys..."), George and Lennie travel together, and George uses "we" to describe their relationship.
The Boss and Curley are distrustful of the traveling pair. The Boss thinks George is stealing Lennie's money, but George says:
I knowed his Aunt Clara. She took him when he was a baby and raised him up.
And George says to Curley:
[George] "We travel together."
[Curley] "Oh, so it's that way."
George was tense and motionless. "Yeah, it's that way."
Later, when describing the American dream, George defines it as shared and collective, including such lower-classes as the mentally-challenged (Lennie) and the physically-handicapped (Candy). In this way, George is like ideal America: inclusive, pluralistic, and affirmative.