Thinking about the theme of loneliness, in the book Of Mice and Men, how does this quotation "No Lennie. I ain't mad. I never been mad, I ain't now. That's a thing I want ya to know" show us that George or Lennie is presented in a lonely or isolated way?
Lennie has just inadvertently killed Curley's wife. Like the other times he has gotten into similar trouble, Lennie runs off and hides by himself. Lennie is socially inept, he panics, and unintentionally hurts others. This leads him to literally remove himself from society. The result is that he alienates himself and is therefore, all alone.
When George finds him, they go through their regular banter that follows one of these incidents. Lennie needs them to repeat these same discussions because they are familiar to him. George says he would be better off if he was on his own. Lennie says he may as well just go live in the hills by himself. After these threats of self-imposed loneliness, George says how they should stick together. Knowing this is the last time he will tell Lennie about the farm (and the rabbits), George is more solemn than usual. He wants Lennie's final thoughts to be about their friendship and the rabbits; not about loneliness. This is why he says he has never been mad at Lennie. George is trying to erase all thoughts of loneliness and sorrow from Lennie's mind.
In a sense, Lennie has always been isolated. George has made it his responsibility to try and watch Lennie in order to integrate him into society. But by this point, George realizes he simply can not watch Lennie enough. George leaves Lennie with pleasant thoughts. He kills him because he simply can not think of a way to keep Lennie safe and happy anymore. Had he left Lennie alive, he would have been killed by Curley or sent to jail: terrible and lonely outcomes