In Of Mice and Men, George and Lennie are peas in a pod, two sides of the same coin, too sides of a man's brain. They are foils of each other: one big, one small; one naive, the other experienced; one a child, the other a parent. To use Freud's terms, George is the Superego (the social, moral side), Lennie is the Id (the hidden desire side). As such, they are inseparable.
Both have a strong work ethic, are good workers (though Lennie is better), and are believers in the American dream. George defines them in the first person plural: "we" and "us." They are team; their dreams are shared:
"Guys like us, that work on ranches, are the loneliest guys in the world. They got no family. They don't belong no place....With us it ain't like that. We got a future. We got somebody to talk to that gives a damn about us." Chapter 1, pp. 13-14
Both George and Lennie were single men who worked on ranches and had need of companionship. Each had a limitation in life, one's limitation just happened to actually be the other. They both appear to have a dream of a better life, although their definition of such might be different.
I would look in chapter one for a quote that demonstrates they have a friend in each other. There's one that sounds like this, "Cause I got you," and "I got you." These words might be in italics in your book. They would be near the idea of their dream to live off the fatta the land.