In the book "Of Mice and Men" Candy is all alone. He has worked as a ranch hand all of his life. He traveled from ranch to ranch and worked alongside other men just like him. There was a friendship among the workers but as they moved on the friendships did not last. Each man was only as good as the weight he could pull on a job. Candy's hand was mangled and he could not do the same work anymore. He is older and sits in the bunkhouse alone all day. The only thing he had that loved him back was his dog. The men put his old and smelly dog down, leaving Candy now totally alone and lonely.
Curley's wife is surrounded by men but has no friends. Curley is very jealous and can not stand her to even talk with any of the men. To the men she is dangerous because she can get them into trouble with the hot tempered Curley. She lives in a world where men control everything. She is dependent on Curley and his father for everything. She lives on a ranch and has no female friends. She is married but spends most of her time alone and sad.
Lennie is not really lonely. He has George and he is less aware of what loneliness means. His simple mind does not allow him to dwell on being lonely. He has George who looks after him and keeps him on track. When George goes to town he talks to Candy and the black man and fills his time.
Crooks was a lot like Candy and the other men. He went from place to place self-isolated from others by the nature of what he did for a living.