How can I analyze the character Patrick in Roald Dahl's "Lamb to the Slaughter" using the PIES model?

The short story "Lamb to the Slaughter" by Roald Dahl begins with a description of a seemingly happy marriage.  Mary Maloney sits alone in her living room eagerly waiting for her husband to come home.  Mary's marital bliss is made clear by Dahl's description of her anticipation: "Now and again she would glance up at the clock, but without anxiety; merely to please herself with the thought that each minute gone by made it nearer to the time when he could come."  Based on Mary's unwavering devotion, the reader comes to expect a loving demi-god of a husband to walk through the front door.  

However, when Patrick does finally arrive, he does not quite live up to these expectations.  He sits down, takes the drink his wife made him without a word, and finishes it in one big gulp.  When his wife desperately tries to lighten the mood by offering to get him another drink or dinner or even his slippers, he snaps at her with short replies of ("no," "sit down," and "I don't want it"). When he finally does speak, his words are cruel and harsh.  His wife is six months pregnant, but he appears to be leaving her.  There is no apology or kindness in his tone, but rather a cold briskness: "I know it's kind of a bad time to be telling you, but there simply wasn't any other way.  Of course I'll give you money and see you're looked after.  But there needn't really be any fuss.  I hope not anyway.  It wouldn't be very good for my job."  Mary, in shock, goes to continue making dinner.  Patrick responds by yelling, "For God's sake...Don't make supper for me.  I'm going out."  

It is clear from his delivery of this news that all he can think about is himself.  He downs his drink as if he is the one about to receive terrible news.  He insists that she leave quietly to avoid any embarrassment for him at work.  He is also "going out" immediately after delivering this news, leaving her to grapple with this alone after waiting all day for him to come home.  She is completely devoted to him, and he responds with callousness and self-indulgence.  With these descriptions of Patrick's actions and words, Dahl ensures that the reader will not be too aghast when Mary whacks him over the head with a frozen leg of lamb.