Waxing poetic -
In fairness to Laura, it doesn't seem she ever intended to leave Shadow for Robbie. Their affair was purely sexual and filling a void for her while he was gone. That's not to say I excuse her for it, or that it wasn't wrong (it was) but I think she loved Shadow as much as she could have but without his actual presence to distract her, then the loss of her other connection (the cat) the darkness was taking over rapidly. It seems only in death (with a clock ticking) can she actually see her faith/love for Shadow and believe that she might actually deserve his light/love.
“Yet many is the man who would take any version of his lost love rather than leave his love lost. He will say, ‘thank you’ to whatever god sent you back to him.”
Include me in that "many," Mr. Ibis.