How has George and Lennie's relationship changed over the years and who is listening to them while they talk about their dreams?

George tells Slim that he used to tease Lennie a lot.

Used to play jokes on ‘im ‘cause he was too dumb to take care of ‘imself. But he was too dumb even to know he had a joke played on him.

George says he even beat him up.

I’ve beat the hell outa him, and he coulda bust every bone in my body jus’ with his han’s, but he never lifted a finger against me.

George says he’s given all that up. Once he told Lennie to jump in a river. He couldn’t swim, and Lennie and other men were barely able to save him. George felt badly about nearly killing Lennie, and he felt sheepish because Lennie was so grateful for be saved.

Since then, they have become quite dependent on each other. Lennie is physically dependent, as he probably couldn’t survive on his own. But he also is completely dependent emotionally. The mere thought of leaving George causes Lennie to panic.

George often complains that Lennie is a nuisance and keeps him from having a good life. However, it becomes clear that George cares deeply for Lennie and depends on his companionship. Lennie's work capacity is also a source of money and pride for George. We learn near the end that Lennie’s desire for rabbits kept George’s own dream alive.

As for who was listening, the old man Candy listened to them talking in the bunk house. His desire to join them and contribute his savings made the dream actually seem to be within reach. Crooks, the black stable hand, also hears Lennie and Candy speak of their plans.