Come to think of it, I'm suprised Michael didn't have more children with other women after Kay. He could have easily had more sons if he really wanted to.
I think Michael's position would be that he got married once and that was forever. This would tie in with his public Catholicism, because he'd have to admit to some sort of mistake or failure to get an annulment to allow him to marry someone else. None of this would preclude a discrete girl on the side, of course.
