Personally, I believe truth kills and that the widowed husband should not have looked for an answer to his question: Why did she die? The cliche: Curiosity killed the cat is very true in the sense that he was grieving for his pain, and also dreamed about how his wife cheated on him. When someone dreams about doubt, isn't in real life-- one's doubting about someone's actions?
the short story is very interesting. the man is so consumed by his distraught, so caught up in the fact that she is gone, that nothing else matters anymore. Sometimes the truth is left unexplained because the truth is too harsh - too real to face. And as for dreams, in my psychology courses i am taking, they believe that dreams are the key to our subconscious. They show what we are truly thinking in real life.
Was he looking for answers to how she died? Or was he only seeking to be near her, to hold onto her, to recapture something of what he had had with her in life, by spending the night in the graveyard? It was an impulsive move, it seems. He was driven by grief and the madness of grief to do so. That's how I read it. Then, was what happened there that night a dream? I think we're being invited to question whether it was or not. Did our narrator see the dead rise and expose the lies? Or did he just imagine it, driven by some secret doubt? He doesn't seem to have harbored any doubts about her. Certainly it is true that the lines that immortalize us once we're gone do not paint the whole story of our lives. We all of us do many things we are not proud of, but these are not the things that appear in the newspapers when we die, these are not the things read out at the memorials or carved into headstones. Perhaps the author is inviting us to each consider our own lives in this respect?