Tom was more Fredo and Sonny's age than Michael's, plus Michael was away at war and college for a number of years. He wasn't involved in the family business, and Tom, Fredo and Sonny all were. They spent an enormous amount of time together. And, as DC stated above, Tom was extremely devoted to Vito. I would think that he definitely felt a sincere and deep sense of love and family for Fredo. I picture Tom as the brother caught in the middle, his love to Fredo, his loyalty to Michael. It was a horrible position to be in.