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Sonny treated Tom shabbily before that family dinner ("Pop had Genco, look who I got") but he apologized immediately. Michael dissed Tom several times and didn't apologize once.
That's a key to understanding the relationships. Tom yells at Sonny, Sonny yells at Tom, but it's more like two brothers fighting, and Sonny as you note immediately feels bad and warmly invites Tom to dinner, and says "Mama" made dinner, not "My mother made dinner." You can tell he's genuinely remorseful for snapping at Tom and knows he hurt his feelings. Sonny may have been a bad Don but he was a human being.
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I quite agree with what you say about Sonny. He's a hothead who speaks too spontaneously but he never aimed at hurting Tom. Like you say, they yell at each other but are also very comfortable with each other, as is shown also in that flashback scene at the end of G2.
In the "Look what I've got !" scene, there was something to explore with the inkling that Tom might not be the consigliere he needs during wartime (and yet, he had some good advice that Sonny should have heeded), but the reflexion stops and is forsaken when Sonny realises he is more or less telling his adoptive brother : "You are not one of us." The priority for Sonny is his family; he cares about his brother Tom a lot more than about the restructuration of the organization.
Contrast that with Michael in the boathouse scene. He coldly aims at hurting. The mistress comment was deliberate, not a case of speaking too quickly and not meaning it.
However, I think Michael 's reasons are more complex than just not having a "single bone of love in his body for Tom. "
It is possible at that moment he is not able to love, and yes, he has never been that close to Tom, but still ...
He has been betrayed and is hypervigilent and paranoid, only looking for any sign of betrayal. This distorts his judgment.
He needs Tom but can only express it through bullying.
At that moment, he also clearly favors Al Neri ( who represents efficient vendetta) than the lawyer Tom Hagen ( who represents legitimating business, which is lomg, full of setbacks for which Mike has no patience).
I also think that in Michael icy/numb mind, the spat with Tom is settled when speaks Italian with him. "Allora, tu stai ? Si, Io sto".
Not for us ! That's far from settling the indignity inflicted upon Tom and the lack of appreciation for all he has done, but in Mike's mind, unable to feel empathy at that point, he might be satisfied that he can trust Tom. No he has no remorse for how unfair he has been.
I always wondered if he found back some of his humanity down the road, long after Fredo and Kay's betrayals.
