I would say that the relationship between them is one based on caring and nurturing. I think that they both need each other in an immediate and powerful way. This is fairly evident with Lennie, as he needs George to look after him and ensure that he is not manipulated. Lennie's aunt implored George to do as much. I think that George needs Lennie as much, though. George is constantly haunted by the feelings of his own banality, his own failures. Lennie's presence reminds George that in someone's eyes, he is extraordinary. The dream of the farm is a comforting thought to both on different levels and their shared affinity for it helps to bring to light how powerful it is to have dreams. Their relationship is the reason why this dream is shared. I think that we can see the exact nature of their relationship at the end of the novel. Lennie's visions and hallucinations speak what George would say, almost absorbing George's words as a part of his own psyche. At the same time, when George has to kill Lennie, it is done out of love. I think that it is done because George would not want to watch and see what the mob will do to him. If George had not loved Lennie, if there was not a strong relationship present, he would have left Lennie to his own devices at this most critical moment.