After reading the responses to the "If a man doesn't spend time with his family...." post I began to wonder if anyone else thought Tom having a mistress was just thrown in the film for shock value. I always thought it was out of character for him. He is so straight laced.

I could be wrong (please let me know) but I don't believe any hint of Tom cheating on his wife was ever mentioned in the book. I do remember the book mentioning that Tom knew the Don never approved of such affairs. Tom was always immensly eager to please the Don and would never do something he would disapprove of. Tom's respect of the Don also led me to believe that this was something that was instilled in Tom, not something to be forgotten over a woman.