In the context of the "Lamb to the Slaughter," what drives people to betray? How did love contribute to Mary Maloney's decision to violently attack her husband? Cite evidence from this text, your own experience, and other literature, art, or history in your answer.

How should we like it were stars to burnWith a passion for us we could not return?If equal affection cannot be,Let the more loving one be me.

W. H. Auden's poem suggests that, when two people cannot love each other equally, to be the more loving one may actually be the easier position. This partner has a life full of meaning and purpose to make the beloved happy.
In "Lamb to the Slaughter," it is clear that Mary Maloney adores and idolizes her husband. She makes him the center of her life—to a dangerous extent. What is the center of his life? We are not told, but it is no longer Mary, if it ever was. She sees his departure as a betrayal and instantly snaps. Congreve, in The Mourning Bride, famously wrote:


Heaven has no rage like love to hatred turned
Nor hell a fury like a woman scorned.


This is certainly true of Mary, who acts with all the passion of her former love in striking down her husband. The lack of emotion she feels after killing him is readily explained by the fact that her love turned to hatred before she killed him. If he had been killed in a car crash on the way home that night, she would have been devastated. As things stand, he killed her idol with his rejection of her love. She merely killed the traitor who murdered her love for him.
Neither Mary nor her husband would have been likely to see their own actions as a betrayal. We do not know his motivation, though it may well have been the boredom and sense of pointlessness caused by being in a relationship when one is adored without being adoring. Mary's motivation, the fall of an idol and a love turned to hatred, is all too clear.

The phrasing of this question is interesting because it's pushing the response toward explaining Mary Maloney's betrayal. In a way, that is easy. Mary doesn't betray her husband. He betrayed her. The other simple answer is that Mary betrayed Patrick because he betrayed her first.
The narrator makes it very clear from the beginning of the story that Mary is deeply in love with Patrick. She is the quintessential doting wife. She is patiently awaiting his return, and when he does return she greets him with a smile, takes his things, and hands him a drink. The text says that she loves "to luxuriate in the presence" of Patrick. Unfortunately, for whatever reason, Patrick's feelings for Mary have grown stale. Readers don't know exactly what he tells her, but it's clear from the snippets of conversation and her reaction that the marriage is over. Patrick betrayed her and his wedding vows.
Mary is shocked and hurt to the point that she isn't in control of her actions right after Patrick's heart breaking news. She moves to the freezer in a trance, and she is almost unaware of her actions.

Everything was automatic now-down the steps to the cellar, the light switch, the deep freeze, the hand inside the cabinet taking hold of the first object it met.

Mary doesn't snap out of this daze until after Patrick's head hits the floor.

The violence of the crash, the noise, the small table overturning, helped bring her out of he shock.

The initial question asks about what drives people to betray. In terms of this story, I think Patrick's motivation for his betrayal is that he could feel stifled by Mary and her constant hovering and attention to his every need. It sounds wonderful to have somebody love you so deeply that they refuse to you leave you alone, but it's likely exhausting and frustrating. This concept is explored in another short story called "The Chaser" by John Collier. The main character desires a love potion that will make the girl that he is attracted to have no other wants or desires other than to please him. The potion dealer sells this particular potion for a dollar, but he sells the "chaser" potion for much more money. The chaser is a poison that kills without leaving a trace. The potion dealer knows that everybody who uses the love potion will for sure come back and pay the higher price because that person cannot stand to be loved so incessantly. It's possible this is how Patrick feels. To his credit, he honestly tells Mary what he's thinking/feeling instead of killing her with some kind of poison.