There is of course the scene near the start of Part II where Michael tells Tom he loves him and has left him 'out' of the business to protect him, but this is contradicted by various other scenes of Mike being cold towards Tom both before and after this scene. The way he tells Tom he is 'out' in the first film is ruthless.
Frankly, I think Michael knew which buttons of Tom's to push. He knew how to make Tom feel terrible, and he also knew how he could command Tom's respect. The way he makes Tom the Don isn't an example of two brothers reuniting after a period of emotional distance, it's an example of Michael ruthlessly toying with Tom's emotions to get what he wants. By the end of that very brief conversation, when Tom seems to me to be on the verge of being overwhelmed by emotion that Michael really does love him, I think Tom would have done literally anything Michael asked. But frankly, I think it's one-sided. Michael isn't sincere, he just knows how to reinforce Tom's loyalty.
