He finds this latter possibility, murder, intolerable, so he tries not to think about it.
This plus the narration of his work habits, his payment of bills on time, etc. add up to tell us that Ben is a good guy - he is just fully in the grip of alcoholism and can't break free and has thus given up trying - that is if he ever did try. Perhaps he just got worse and worse and went very slowly from functioning to non-functioning alcholic.
