Connecting Lenny and Candy's dog

By the river bank, George has the gun on the back of Lenny's head, about to pull the trigger, but he stops himself. Why is that? I think he has a very hard time killing his companion, because he has been with him for so long, and is attached to him. We also saw this with Candy, and his dog. Yet, Candy was not the one to end the dog. I think George certainly had the opportunity to let Curley, Slim, or Carlson do the job for him, like Candy did. I also think that it would be much harder to kill a human companion, than a old dog companion. George probably felt responsible for the troubles Lenny brought to the working men, and their lives. George wanted to be the one to help Lenny steer away from what could happen to him. George knows if he doesn't kill Lenny, he would face a much worse ending, from the other men. Just like how the men claimed it was worse to keep the old dog alive. In the end George was forced to pull the trigger because "There were crashing footsteps in the brush now." (106). Just like Candy was pressured by Carlson, George was forced to pull the trigger sending a bullet into the skull of Lenny, killing him quick without pain. Maybe if the men did not come looking for them, George could have let Lenny go, but George finished the job quick, just like the old dog.