When George loses his ear, he's upset because they can no longer use their favorite joke. Fred's upset because he can't get rid of the terror he felt when he thought he'd lost his twin forever. George doesn't really understand.
When Fred falls in battle, George finds that he understands all too well.
After George loses his ear, Fred briefly considers cutting off his own ear so they'll match (because he doesn't want George to bear the pain alone). George can tell what he's thinking and yells at him for being an idiot.
After Fred dies, George considers jumping in the coffin with him (because he doesn't think he can bear the pain of being alone). No one's there to yell at him, so he stands in front of a mirror and yells at himself.