Talk about watching a movie and missing the whole point. George was a weak and ineffectual coward who just didn't have it in him to bash Dickie over the head with a shovel. Even when George shoots Dickie towards the end, he's shocked at his own actions, as though he doesn't believe that he really did it at all.
Exactly. George is a meek, little man & he's bitten off more than he could chew: Left his old wife Agnes & took a young gorgeous wife, Theresa, to go live in a castle. But, he's not the heroic type and Theresa cheats on him & he knows it. Dickie even calls George a cuckold. In the end, Theresa leaves him (after 11 months of marriage), he breaks down & calls out "Agnes" because he screwed up his life.
That "Agnes" was very much in the vein of "Rosebud", but much sadder & more anguished. Great ending.