Lennie said, “I thought you was mad at me, George.”
“No,” said George. “No, Lennie, I ain’t mad. I never been mad, and I ain’ now. That’s a thing I want ya to know.”
The tone to this exchange is essential. Lennie is expecting anger but, understanding that these are Lennie’s last moments, George is calm and sad. Trying to put Lennie at ease as much as possible, George wants to make sure that his friend knows that he was always his friend, hence his reassurance that “I never been mad”.
Lennie said, “George.”
“I done another bad thing.”
“It don’t make no difference,” George said, and he fell silent again.
George is resigned to Lennie’s death here. He seems fatalistic, as though this was always going to be the outcome to their friendship. He says, “It don’t make no difference”, explaining that the future now only has one outcome, regardless of what happened in the past.
Slim came directly to George and sat down beside him, sat very close to him. “Never you mind,” said Slim. “A guy got to sometimes.”
Slim, unlike the other ranch hands, understands the situation George finds himself in, and reassures him that he had no option but to shoot Lennie.