Lennie and George stick together through everything. When Lennie is accused of assaulting a woman, George helps him escape so that he isn't hurt by the townspeople (or worse). The fact that George has stuck with Lennie for so long puzzles their coworkers. George also guides Lennie on how he should speak and carry himself. Towards the beginning of the novel, George directly tells Lennie to get rid of the mouse that he's holding onto. While Lennie is extremely resistant at first, he eventually gives in and takes George's advice. Their devotion to each other is seen most clearly in the closing pages of the book, when George shoots Lennie. While this action can be interpreted as cruel, it's much more humane when compared to Curley's threat to lynch Lennie. Instead of leaving him at the mercy of Curley, George shoots him.
[P1] George and Lennie have remained close friends through many life-altering experiences. [P2] George looks out for Lennie and helps guide him through life. [P3] Lennie looks up to George. [P4] George shoots Lennie so that he will not be tortured by Curley and his gang. It is a sympathetic action that shows his true devotion to Lennie.