Patrick Maloney is a pretty despicable husband, as evidenced by the details below:

He is a man who needs to be taken care of. In itself, this isn't the most horrendous detail of his character. But within the context of his deception, it is notable. When he gets home, he awaits his wife as she prepares his drink. He allows her to collect his coat. Mary quietly waits for him to acknowledge her, as "she knew he didn't want to speak much until the first drink was finished." He has established himself as the dominating presence in this household, and his wife is expected to cater to his needs.

He's a good liar. Mary did not see this conversation coming. Her stunned response captures the way her husband has been deceiving her for quite some time:

Her first instinct was not to believe any of it. She thought that perhaps she'd imagined the whole thing. Perhaps, if she acted as though she had not heard him, she would find out that none of it had ever happened.

We can assume (based on his wording) that Patrick has been involved in an affair for long enough that he's developed a bond strong enough to leave his wife, yet he carefully hid all the details from her, leaving her in shock when he finally tells her the truth.

He's a hypocrite. Patrick is a policeman, sworn to serve and protect citizens from harm. Yet in his own home, he is unfaithful to his wife and decides to leave her when she's six months pregnant. And to add insult to injury, he asks Mary not to make any "trouble," because "It wouldn't be very good for [his] job."

Patrick's character is inexcusable, especially considering his wife's adoration of him.

Patrick Maloney is the essence of a consistent individual. Every day, he returns home at the same time and goes through the exact same routine—asking his wife for a drink and consuming it, never complaining about his day or much at all, just remaining seemingly content and complacent about life.

His ambivalence and consistency are what lead his wife to realize something must be wrong—because he breaks his routine ever so slightly. When he tells his wife he is leaving her, we learn slightly more about his persona. He seems to be an analytical person who thinks that having his soon-to-be ex-wife provided for financially is enough to mitigate the situation, and he seems to care little for her feelings. He is something of an automaton with little care or compassion toward his wife.

The reader learns at the beginning of the story that Patrick is punctual and predictable. He arrives home at the same time daily and always has a drink when he arrives. His actions are so predictable to Mary that she notices subtle differences. For example, she is aware that he finishes his drink more quickly than he normally does. She learns the reason for this when Patrick announces his intent of leaving her. The reader also becomes aware that Patrick does not often complain or voice his displeasure. This may be part of the reason she is so surprised by his announcement.

Once Patrick makes his intentions known to his wife, the reader can make other inferences regarding his personality traits. He is straight-forward and only takes a few minutes to talk to his wife. Although he does say he will see that she is taken care of financially, one can assume that he must be somewhat selfish to leave his pregnant wife. This trait is also seen when he states that he hopes for no trouble because he doesn't want his job to be affected.

This question is tougher than it first appears, because Patrick Maloney is barely in the story. Well, he's in the story the entire time. He just isn't alive for much of the story.  

I would pick cold and selfish as the two leading character traits to describe Patrick. The reason I think that Patrick has both of those character traits is because he bluntly tells Mary that he is leaving her or divorcing her. He knows that she loves him dearly. He knows that she is pregnant. He even admits that his news is bad timing.  

"And I know it's a tough time to be telling you this, but there simply wasn't any other way."

Despite knowing all of that information, he still is willing to just walk away from Mary and his life. I can only imagine that his reasons are self-serving. Leaving your pregnant wife for selfish reasons is the definition of cold.