I could be wrong, but in my opinion the husband was purposefully looking to have an affair, but had to claim that it was the nurse's fault after his wife caught on. If a man wants to have an affair, he will eventually find someone to have an affair with. Someone should warn his wife that he's not worth it.
And about him firing her because he was afraid he would have an affair with her... Wouldn't she have the right to say no? Unless he was planning on forcing himself upon her, she could have just refused his overtures, and they could go on with their lives. As I said, I could be wrong, but he sounds a bit predatory to me.