What could be the reasons that Patrick decided to leave his wife?
We are not really told why Patrick Maloney would want to leave his wife so we can only guess. I think that the most likely reason is that he is bored with her and that he wants someone who will be a bit less subservient and uninteresting.
From the first part of the story, it seems that the two of them have a pretty set routine. He comes home and then she waits on him -- gets him everything he wants, etc. She is content just to sit there and be with him and she seems to do so adoringly.
I know this sounds terrible, but I think that he has gotten bored with that. He wants someone who will treat him more like an equal. Maybe someone who will not just sit there and adore him. I think that he has started to take her for granted because their life has gotten so boringly consistent and because she always acts so much like a servant to him.
For some reason I always got the impression that Patrick left his wife for another woman. It was the first reaction as to why she would snap the way she did. Otherwise, I imagine that she would have tried to find a solution to the problem. To me, the shock must have been so profound that it literally moved the earth beneath her. Another thing that comes across clearly is Patrick's arrogance. Somehow he inspires dislike even before he did what he did. Perhaps is the hero-complex that often comes with working dangerous jobs like he did. However, between his arrogance, his lack of care, and perhaps with someone in the middle, he found no problem telling his wife off. But she got the last word ;)