There is a mutual conflict between Curley and George because Curley is seeking trouble with Lennie. Curley doesn't like big men because they make him feel inferior.
Lennie and George are trying to achieve their dream, which is to own a piece of land all their own for them to live on. However, the circumstances are hard for this dream to be achieved, and also, lonely ranch men are supposed to work for all their lives.
George sometimes thinks that being responsible of Lennie is such a costly burden and thinks that without him everything would be perfect, yet he does care about him and tries to help him which generates an internal conflict in George.