Why did Mike insult Tom in 2nd part many times?
Mike told him to leave when he was talking with JOhnny Ola. Also in the scene were Mike decided that he was going to kill Roth, Mike insulted Tom a few times...

Why is this?

One reason, at least, for the snub at the Johnny Ola meeting, was that Mike did not want Tom in the loop about certain of his dealings.

Remember the boathouse scene later that evening, after the assassination attempt, when Mike tells Tom something to the effect that he (Michael) knows he has hurt Tom by excluding him at times, but because Tom did not always know exactly what was going on, Tom was now the only person Michael could fully trust.

In other words, if Tom did not know about Mike's dealings with Roth, he could not have been the one to betray him to Roth.

Juventus, my belief has always been that Michael, rightly or wrongly, blamed Tom for some of the misfortunes that befell the family. I think he felt that Tom was partly responsible for Sonny's assassination because Tom failed to uncover the connection between Carlo's beatings of Connie and the plot to kill Sonny. He may also have seen in Tom, whose training was as a lawyer, a "weakness" (my word) for negotiation vs. action--for example, Tom urging Sonny to make the deal with Sollozzo, and Tom arguing against killing McCluskey, even though leaving him alive represented a mortal danger to Vito. Tom also failed completely to find out that Frankie Pentangeli had survived--which meant that Michael had opened himself to five counts of perjury in his Senate testimony. That one was really bad.

When Michael said to Tom that he was "out" because he was not "a wartime consigliere," he was stating a conclusion that Tom had come to about himself. In the novel, after Tom learned that Sonny had been killed but before he told Vito, Tom had a moment of self-reflection in which he concluded that "he was not a fit wartime consigliere--old Genco would have smelled a rat."

There are dramatic reasons for the insults to Tom, too. Michael leaving Tom out of the negotiations with Johnny Ola reinforced just how far Tom was "out." It also set the stage for that magnificent scene after the shooting in which Michael plays Tom like a violin, telling him that he's the only one he can completely trust, and putting him in charge of the family (temporarily)--only to revert back to insulting and abusing Tom after he came back from Cuba. A very effective vehicle for displaying how Michael's character had evolved.

I always felt sorry for Tom in that scene. Although Michael later explained to him why, Tom was always loyal and I don't think he deserved to be spoken to in that manner. Then again, that's Michael's way I guess.

TIS

I like the scene when he returns from Cuba and is talking to Tom. He gets angry very fast upon hearing of the miscarriage of Kay. He says something in the effect of can't you give me a straight answer anymore? To me that line suggests of Michael blaming Tom for the current problems the family faces and out of frusturation too.

Also, Mike alienated Tom the most, blaming him for the misfortunes of the family, this is basically part of Michael's elivation to bastard.