The scene when Tommy gets the news that Arthur will be a father, I interpret it as follows, Tommy realizes that he will lose Arthur, the only person that was on his side from childhood, and after his wife died, he is truly the only person Tommy leans on (besides Paulie). Now, Arthur being a father, Tommy realizes that he might not be no.1 in his brother's life, and maybe, Arthur will be a good man, thus Tommy would not be able to afford to implicate him as his right-hand hound that he unleashes on his enemies. The look on Tommy's face is a mixture of his happiness for his brother, and sadness of the realization.
Review of Episode #1.3
