Who is Arthur from Nine Stories and what is their importance?

Arthur is a married lawyer, who works at the same firm as Lee. His wife's name is Joanie. Arthur and his wife live in New York City, but he is considering a move to Connecticut to have more time alone with his wife. He does not trust his wife, and he is not even certain that he loves her, yet, he cannot bring himself to leave her. Joanie, however, is having an affair with his co-worker, Lee.