Hey cut Mike some slack! He wasnt exactrly kicking up his heels for all those many months he was in Sicily, and the way things were going, I think he realized that he would either be there a long time and/or once he got back to New York he would be in the family business and Kay would have moved on. I think he was struck by a thunderbolt when he saw Appolonia and so was she, and had she lived he would have been content to have an obedient Italian wife instead of some shrill American who was always carping at him for not becoming "legitimate" quickly enough, and who ran off to have an abortion because Mike had a "Sicilian Thing," which had to be stopped. Notice Kay didnt mind living in luxury though.
Moreover, Michael was back a year or more before he even bothered to contact Kay, so I have always wondered if he wasnt exploiting her just a little.
In fact I think they were exploiting each other, but thats another thread.