In my book, the 5th page of chapter 4 has a discussion between Crooks and Lennie. Crooks encourages Lennie that since George is out with the guys something could happen to him. George could get hurt or choose not to come back. This makes Lennie mad:
Suddenly Lennie's eyes centered and grew quiet, and mad. He walked dangerously toward Crooks. "Who hurt George?" he demanded.
A true and loyal friend will always be ready to defend their friend.
Another loyalty quote occurs in the first chapter when Lennie breaks in while George is telling how it's going to be:
"... because I got you to look after me, and you got me to look after you, and that's why."
The rest of the quotes in chapter one significantly demonstrate George's loyalty to Lennie because he is doing most of the talking.
George and Lennie have the most beautiful relationship in the book. In fact, they have the only friendship. Moreover, it is mutual. George cares for Lennie, and Lennie cares for George. Since this question is about Lennie's loyalty to George, here are a few examples.
First, in the beginning of the book, Lennie recounts his loyalty and friendship to George. He says that he will look after George and that George will look after him. Here is the quote:
Lennie broke in. “But not us! An’ why? Because . . . . because I got you to look after me, and you got me to look after you, and that’s why.” He laughed delightedly. “Go on now, George!" “You got it by heart. You can do it yourself.”
This quote takes place on page eight in my edition in section one.
The place where Lennie shows his fierce loyalty to George most is when Crooks suggests that George might be hurt. When Lennie, who is mild mannered, hears this, he growls. This is the first time Lennie gets angry. He looks at Crooks with a menacing look and says that no one will hurt George. Here is the quote, which takes place on page thirty six in my edition.
Lennie growled back to his seat on the nail keg. “Ain’t nobody goin’ to talk no hurt to George,” he grumbled.