Adam first meets his new wife Cathy as she is recovering from a very bad beating by her former beau (who she had been hustling, as Cathy hustles everyone). As her scars begin to heal, Adam decides he’s fallen in love with her, and they marry. Fully restored to health, Cathy also finds herself pregnant, and so she’s further hampered in her effort to get on with her plans. As soon as she recovers from giving birth, she packs a bag and holds a shotgun on Adam as she takes off.
Her voice was dead and metallic. “I don’t give a damn what you believe. I’m going.”
“Throw them in one of your wells.”
When Adam tries to stop her from leaving, Cathy shoots him. It is Adam’s turn to recover from a severe physical blow, and the scars he carries on his body as he recovers and raises the boys are a reminder of Cathy’s betrayal.
Since many of the major characters in the novel are aligned either with Caine or Abel, it is further symbolic that a Caine figure (Cathy) betrays an Abel figure (Adam), as a continuation of the same pattern in the Biblical myth of fratricide.