Describe George and Lennie's relationship in Of Mice and Men.

George Milton and Lennie Small have a fraternal and symbiotic relationship.
The small, intelligent man and the large but slow-witted man have a fraternal relationship as well as one of mutual dependency. Lennie is dependent upon George for decisions and direction, while George, who is diminutive, needs Lennie sometimes for protection. He also needs someone to care for and to have as a companion. When the two friends camp in the clearing, Lennie asks George to recite for him the conditions of their relationship and their dream for the future. At first George takes note of how the other bindlestiffs, who have no friends, are very lonely. They have no family and belong nowhere. When they work on a ranch, they "work up a stake," but then they go into town and spend it all. Afterwards, they must start all over at another ranch with nothing to which they can look forward.
But with George and Lennie, things are different; they have a future because they care about each other. George recites,

"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 blowin' in our jack jus' because we got no place else to go. If them other guys gets in jail they can rot for all anybody gives a damn. But not us."

Later, George explains to Slim that he and Lennie are from the same place, and after Lennie's aunt died, George began to take care of Lennie because he is "too dumb to care for himself." George adds that Lennie is a nuisance, but "...you get used to goin' around with a guy like that."
Much like a child, Lennie enjoys hearing over and over the tale of how they will have a small place where they will raise their own food. Unfortunately, Lennie commits such misunderstood acts that he gets George and him into trouble. When Lennie inadvertently kills Curley's wife, there is no chance of running away or escaping fate. George shoots Lennie to prevent his violent death at the hands of an angry lynch mob.
In Of Mice and Men, the fraternity of man is a motif, as evinced in the relationship of George and Lennie, along with the desire for this fraternity in such characters as Candy and Crooks. 

George and Lennie have a rather unique and complex relationship. Both characters have different strengths and weaknesses, yet find a way to develop a mutual friendship that benefits each of them. Although George is physically smaller and weaker than Lennie, he is Lennie's guardian and feels a social responsibility to take care of him. In contrast, Lennie is a massive individual with a mental disability. He looks up to George and allows George to make decisions for him. Despite the fact that George has a tendency to yell at Lennie and criticize him, George truly cares about his friend's well-being. Lennie also understands that he can annoy George, but offers him companionship in an unforgiving world. George and Lennie also comfort each other by discussing their plans of owning a home and a piece of property throughout the story. Their friendship provides each other with a sense of belonging and companionship that other migrant workers do not have.