What is the nature of the relationship between George and Lennie in Of Mice and Men? John Steinbeck's Of Mice and Men

One of the major motifs of John Steinbeck's novella,
Of Mice and Men is the Fraternity of
Men. Writing his work during the Great Depression, Steinbeck the
Socialist perceived the terrible alienation of the migrant worker and felt that the
communion of these men working together was the solution to their terrible
alienation.

Thus, the relationship of George and Lennie is
that of brotherhood.  While George essays to protect Lennie
as an older brother would, he does, in fact, fail at times as would a sibling who
assumes such a role.  While Lennie does fear George somewhat, his fear resembles that of
a younger sibling for an older one, rather than a parent.  For,his perception is clearly
that they are friends, and, thus, equals.  When he asks George to tell him "how it is
with us," and George describes how they have "somebody to talk to that gives a damn
about us," Lennie breaks in describing their reciprocal
relationship,

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"But not us!  An' why? 
Because...because I got you to look after me, and you got me to look after
you, and that's why."

Each man provides
something for the other that he lacks.  With George, Lennie provides love and trust and,
above all, the sustaining of the dream.  For, once Lennie who truly believes in the
dream is gone, so, too, does the dream die, since Lennie is the keeper of ithe dream. 
For Lennie, George is the thinker and the planner.  In their fraternity, there is
strength and happiness, Steinbeck seems to say to his readers. Alone, apart, both
Lennie's and George's ends are
tragic.