The reason Lennie needs George is that Lennie is really forgetful and has a child like mind and he is not that bright meaning that he is like mentally retarded I think. Lennie has a obsession with mice his aunt used to give him mice and he would pet them. But if they bit him he would squeeze their heads and then the mice would die. He is also on the run because he did something in a town called Weed.
I think George is keeping Lennie around as protection so if they are caught he can shift the blame to Lennie and go saying that he threatened me saying if I try to leave he would kill me. I also think that he enjoys the company of Lennie and he is using him as cover because one person is more suspicious than a single person.
