A major theme in Steinbeck's novel, Of Mice and Men, is loneliness. Many of the characters experience loneliness, but some more than others. Candy, Curley's wife, and even George all experience loneliness. Some more than others.
Candy, the ranch's farm hand, is an old man who has nobody in the world but his dog. Since Candy cannot go out to work in the fields, he is left behind to clan and take care of things. He is most grateful for his dog being there. But not everyone feels that way. Candy's dog is old and smells, and the other men on the ranch complain. One of the men suggests that Candy should put the dog out of its misery. Candy says he cant do that. He's had that dog since it was a pup. So they talk Candy into letting someone else shoot the dog in the back of the head so he wont feel a thing.
Candy knows he cannot fight this battle and gives in. They kill his dog, and now Candy suffers a great deal of loneliness.
Curley's wife also suffered from loneliness. She was ignored for her reputation of being a flirt, and the fear of getting in trouble with Curley. She was ignored by the farm hands and her husband. This caused her to seek any kind of attention she could get, even through flirting. I suppose Lenny's killing her put her out of her misery just like the old dog.
The loneliness that George would have experienced is not told in the book, but you know it is there. George has to put Lenny out of his misery, just like Curley's wife, and the old dog. George knows that if Lenny is not...