...BETRAY is the word Michael used when making confession to Cardinal Lamberto "I betrayed my wife, I betrayed myself"...
Killing "your father's son" is betraying not only yourself, but the trust your father bestowed upon you when he gave you control of the "family".
That's all fine & good. None of it negates the fact that Fredo's betrayal of
his brother,
his father's son, is what eventually led to his own demise.
......the look on Michael's face was that of a man who was troubled with the thought, mind made up but Connie's intervention led to him deciding to give Fredo a chance to speak; the next scene was with Fredo and his outburst,...then there was no doubt about what he would do, but its bothering him.
Actually, Fredo's 'chance to speak' and 'outburst' came long before that scene with Connie. And I never saw anything resembling 'troubled' in the look on Michael's face when Connie comes to see him in the boathouse. More like 'numb'.