George and Lennie are friends in Of Mice and Men. George takes on a father-figure role toward Lennie. George ends up being the care-taker from the beginning and throughout the book. He has to ensure Lennie is treated fairly (when the boss wants Lennie to talk, and when Curley wants to beat Lennie up) and follows rules of society (Lennie needs to understand when it is okay to touch people, and if and when it is appropriate to bring animals into the bunkhouse).
Lennie does provide George the fulfillment of George knowing that he is contributing to the world, however, Lennie's disabilities ultimately become too much for George to handle.
This story is truly a story about the lengths to which one will go in order to do what is best for a friend.
george and lennie have been friends since the beginning of the book george has promised lennies aunt that he would take care of him