George needs Lennie to give direction to his life, to avoid descending into the abyss of isolation that he saw all around him. When George says " An’ when the end of the month come I could take my fifty bucks and go to a . . . cathouse . . .” his tone of voice and the choice of Steinbeck’s punctuation makes it clear he could see the emptiness of the freedom he claimed to be losing by being with Lennie. Being alone would make him another victim of the cyclical structure and reduce him to be an ordinary migrant worker. When he says ‘I want you to stay with me’ suggests leading and supporting Lennie gave meaning to George's life, along with some sense of power and control. So without him, he’s just another victim of the cyclical structure with no control over anything.
This was why Killing Lennie was hesitantly difficult, not only because he was killing their shared dream and his close friend but because he was destroying the only thing that made him different from all the other workers. He was destroying his power because he had no one and nothing to influence or control; he’s become an ordinary guy, another migrant worker of the cyclical structure in society. This results to George having no power; he looses his physical power, which was Lennie and the only thing that distinguished him from the others which was also Lennie.
When George sees the emptiness of the freedom he thought he was losing by being with Lennie, Steinbeck revels how during the great depression people were sinking into loneliness but having control and influence over someone or something gave meaning and power to life. Other wise it was just work and sinking deeper into the abyss of isolation.