I understood why andrew and nicky hated each other andrew hated him because when Andrew was facing attempted murder charges in the 80s he needed to borrow money to pay his lawyer fees and nicky would not give him 2k so andrew lost his lawyer and he got convicted. He was also annoyed that nicky did not have some govt witness killed after he testified against andrew.
Nicky hated him because he lost nicky a major sports opertaion when he got arrested in the 80s and he never kicked up money and he told nicky he wanted to be released from his crew.

I hate what he did to the others though like the bank robbery team saved him from nicky and mike helped his family out and when he got out of prison start up