It is possible to make deductions about the development of Steinbeck's novel from an idea into a novella and shortly afterward into a stage play. The author wanted to portray the hard lives of farm workers in California, a subject with which he was quite familiar from personal experience. He needed to focus on two characters and show them traveling from place to place in order to obtain jobs entailing hard labor for basic room and board and a tiny salary.
For many reasons most of the exposition in the story is conveyed through dialogue. One was that Steinbeck was very good at writing realistic dialogue that conveyed information and characterized the speaker at the same time. Other writers of his era who were also noted for their good dialogue-writing were Ernest Hemingway, Dashiell Hammett, and James M. Cain.
Another reason so much exposition is conveyed through dialogue is that Steinbeck intended to adapt the book immediately into a stage play. Since almost all information in a play is conveyed through characters talking to each other, Steinbeck used this technique in the novel so that the adaptation would not only be easy but also faithful to the original.
Naturally he needed two characters talking to each other. Both had to be men because they had to be strong, tough farm workers who slept in bunkhouses. He wanted these two to share a dream of owning their own dirt farm. But this raised questions about their relationship. Many students have asked e-Notes about the relationship between George and Lennie. A few have even asked if they were "gay."
Why should two men want to share a farm when the normal pattern is for a man and a woman to own a farm, have children, and let the children care for them when they grow old? Steinbeck had to invent a reason. Maybe one man was handicapped and the other looked after him. But how could an invalid do hard field work? Maybe he was mentally handicapped but exceptionally strong and quite capable of hard labor. George has to explain everything to Lennie, and thus he is providing exposition to the reader as well.
This was probably how Lennie was born. George has to tell him what to do, but Lennie provides George with companionship and protection.
George (and his creator Steinbeck) seem defensive about the relationship--as if trying to make it clear that they are not "gay."
In Chapter 2 the boss asks George:
"Say--what you sellin'?"
"I said what stake you got in this guy? You takin' his pay away from him?"
Then in Chapter 3, Slim tells George:
"Funny how you an' him string along together."
"What's funny about it?" George demanded defensively.
Notice how George is demanding defensively. He has been asked this question before. Other men have wondered about the relationship--although they don't even know that George and Lennie share a dream of jointly owning a farm. Steinbeck uses Slim's questions to have George explain how he and Lennie became traveling and working companions.
"It ain't so funny, him an' me goin' aroun' together," George said at last. "Him and me was both born in Auburn. I knowed his Aunt Clara. She took him when he was a baby and raised him up. When his Aunt Clara died, Lennie just come along with me out workin'. Got kinda used to each other after a little while."
George and Lennie are definitely not gay, yet George is taking on a heavy responsibility and depriving himself of any chance to live a normal life with a wife and children and a little farm of their own.