What keeps Lennie and George together in Of Mice and Men?

One of the most powerful elements in Steinbeck's novella
centers on the idea that shared subjective experiences can provide solidarity between
people. For example, part of what causes Crooks the most amount of pain is that he is
isolated as a person of color, incapable of forging these shared experiences with
anyone.  For Lennie and George, the shared experience of hope is what binds them.  This
hope is what drives the belief that after a certain point, Lennie and George will be
able to "get out" of the life of living as bindle stiffs, moving from ranch to ranch. 
This is the hope that drives both of them.  George's hope is that he can own something
and be his own boss, while Lennie's hope is to "take care of the rabbits."  It is this
collective hope that binds them to one another.  From the opening chapter all the way
through, this vision is what allows both of them to remain in belief of the other.  Even
at the end, when George has to kill Lennie, this vision of hope becomes more poignant
when iti becomes Lennie's last vision.