Describe Patrick's characteristics. What textual evidence does the author use to describe him in order to achieve this effect?

In the opening paragraphs of the story, the narrator describes Mary's perception of her husband. She adores him. She watches the clock with pleased anticipation because each moment that passes is one moment closer to when Patrick will come home from work. When he gets home, she waits on him, taking his coat and getting him a drink. This is their ritual. She loves everything about being in his presence: 

She knew he didn't want to speak much until the first drink was finished, and she was satisfied to sit quietly, enjoying his company after the long hours alone in the house. She loved the warmth that came out of him when they were alone together. She loved the shape of his mouth, and she especially liked the way he didn't complain about being tired.

Given the way the narrator describes Mary's admiration for her husband, the reader would assume that he is a good husband, one deserving of Mary's praise. However, he behaves coldly toward her in preparation for giving her the news that he is leaving. He says this pretty flippantly. If this is any indication of how he'd always treated her, he never deserved such praise. He promises to give her money (she is pregnant) and selfishly says he hopes the break-up won't be a problem because it wouldn't be good for his job. 

First, the author describes Mary's extreme admiration for Patrick. This helps the reader understand Mary's shock when he gives her the news that he is leaving. The reader has the impression of a good husband and is then presented with a selfish adulterer. The reader then can understand Mary's shock. The subsequent shock (to the reader) is how Mary reacts.