The something it reveals is typical of any siblings who regret not spending more time together. But how do you read anymore than that into it? Fredo's statement about being left on the doorstep indicates his feeling of inferiority which Mike has already recognized. But it would be quite a leap for Mike to detect more than that.
No it is more than that. What you describe is more like what went on between Connie and Michael. She also was mad at him and she also was estraged from him, but when they hashed it out, there was real compassion, and she became his caretaker. With Fredo the statements that he was mad, and the rhetorical question , Why didn't we spend time like this before is a thinly veiled admission of his treachery.
