DMC, I'm stretching here, but I think that being hit by the thunderbolt represented Michael having no control over things--he just got clobbered. And then Apollonia was murdered. Now, I know and you know that her death wasn't as a result of Michael not controlling his emotions and his environment. But her death took a lot out of him emotionally. He may have blamed himself, in part, because he was the target. So, after that, he became more controlling. While I think he loved Kay in his own (limited) way, he was using her as a stepping-stone to "respectability."
plaw: I meant what I said literally about Sonny and Lucy having "something" of a real relationship. The something could have been pure sexual attraction, but it was more than just an occasional quickie.