I have said before that as much as she protested, Kay enjoyed the privileged lifestyle Michael gave her. She very well knew what his business was, and I agree with the others that she was totally in denial and deceiving herslf.

Only when her life and her children's lives were threatened did she beging to pull away, then with Michael skipping Christmas to go to Cuba, the abortion and Anthony's decline she decided she had enough.

But as we see in GF III she always loved Michael despite his faults, and Michael, while claiming he loved her, probably merely wanted to possess and control her more than anything else.
If Michael loved anyone it was his daughter Mary. His words to VIncent were prophetic "they come after the ones you love."