Loneliness is a basic part of human life. In his novel, Of Mice and Men, John Steinbeck illustrates the loneliness of California ranch life in the early 1930's and shows how people are driven to find friendship.
George and Lennie would truly be lonely if they did not have each other. They consider each other family, even though they are so different. To George, Lennie is like a pet or a little brother, because George turns to him for friendship and someone to talk to. George's frequently shares his philosophy about guys that work on ranches. 'Guys like us, that live on ranches, are the loneliest guys in the world.' He means that if not for each other, then they would be all alone, with no friends.
Curly's wife is lonely because of someone else, Curly. Everybody is afraid to talk to her because Curly is extremely jealous and would start a fight.
She is always flirting with the workers, because she does not like Curly and is looking for companionship. She even talks to Crooks, Candy and Lennie in the barn, when nobody else would. Then, when she spots Lennie in the barn alone, she tries to get him to listen to her, even when he does not want to talk. She is obviously very desperate if she wants to talk to someone as dumb as Lennie.
Candy also has his one friend in the world, his dog, whom he can not even talk to him. However, when his dog dies, he has to look elsewhere for friendship. He hopes that these friends can be George and Lennie. He asks George if he can join them in their quest to own a piece of land and live off it. Candy also needs to share his thoughts with them.