And he promised her that he was a different man than his father, that he was going to change the business, move the family out of NY, to that nice clean air, and make his money as a legitimate man who owned shares of hotels and stock in AT&T. But he lied.
Yes he did--he owned stock in ITT, not AT&T(my former employer, AT&T, would never have let a gangster like him own shares.
So, I think that Kay miscarried (abortions were incredibly difficult to come by, especially for someone watched over as closely as Kay), and told him the two things he could never forgive - that it was an abortion and, worse, that it had been a son. She was hurt, and she wanted to hurt him back in the worst way.
Though abortion wasn't legal until after
Roe v. Wade in 1973, most women or girls with a few hundred bucks could have gotten an abortion, and from a medical professional in a sanitary setting. But, I agree that Kay's confinement to the compound would have made it difficult. Even more difficult: what Dr. in his right mind would perform an abortion on the wife of Michael Corleone? So, I think miscarriage, with lies about abortion to hurt Michael, is more probable. Also, amnneocentesis was unknown in the US in 1958--how could she have known (at three months, per Tom) that it was a boy? She said it to hurt him.
Just remember the look she gave him the night of Anthony's communion party after the shooting. IMO, that was the end of their marriage.
Yes, indeed. It was all over, right there and then. If looks could kill...