I am of the opinion that Michael did love both Kay and Appollonia, but unlike most people marriage and family were not as high on the priority list as his business and strive for power.

Yet, I think even tho he loved Kay, he probably considered the fact that it would look good to have a wife/kids to give the appearance of a "good family man."
I too, would not have waited for Michael. However, Kay knew what kind of family he came from and she chose to wait for him and then later she chose to marry him even after he told her he was in the family. I don't know if blame is the right word, because we all make wrong moves and do stupid things when it comes to love. I prefer to call it a "life experience," not a good experience but still a life experience.
I still say, even though both ladies were good wives to Michael (I know we didn't get to see Appollonia as a wife for long, but I am judging by her culture/heritage at that time in Sicily), Appollonia would have made a better wife for Michael, for the simple reason that she wouldn't give him "flack"....I ;am not saying that made her a better wife than Kay, but the better choice for Michael. Sicilian women (like mama), would know when to keep quiet and when to speak. And to be married to Michael I think you'd have to understand and accept that.
TIS