Michael and Kay's marriage was always a little rough, but the fact is, they both always loved eachother. Kay, I believe had the abortion just so that she could get as far away as possible from Michael. She had a part of Michael in her, a part of Sicily inside of her (note that it just so happens that it was during Michael's senate hearings that she aborts the baby). She knows Michael is cold and ruthless, and, as much as she loves him, she can't stay married to him. And as much as she loves Anthony and Mary, she can't bare another child of such a cold man.

And, to Michael's wondering if it was a boy, you have to look at where he grew up. What if Vito only had Connie and Fredo, then where would the family be? What if Vito only had Connie and Santino (who by GFII is dead), then where would the family be. Maybe Michael knew, that as hard as he tried, he would never break free from the Mafia, but even if he did, you wouldn't want someone like Fredo running a casino, or any business for that matter. Sorry, Fredo... rolleyes

"I never wanted this for you. I work my whole life--I don't apologize--to take care of my family, and I refused to be a fool, dancing on the string held by all those bigshots. I don't apologize--that's my life--but I thought that, that when it was your time, that you would be the one to hold the string. Senator Corleone; Governor Corleone."
-Don Vito Corleone to his son, Michael