There are a multitude of pet owners who have regretted NOT being there with their pet when the pet was being euthanized, and their feelings that they may have abandoned their pet at a crucial time has created
a certain sense of guilt that simply will not go away.
That
sense of guilt and / or discomfort coupled with a
certain morbid curiosity goes a long way to heightening the impact
of the admittedly rudimentary and melodramatic turns to be found in Baker and Chris Bergoch's screenplay.
He is also, at that point in his life, overly conscientious, perhaps because
of his own repressed
sense of guilt, so he finds her reckless for having the gun, smoking, or using
certain words in front
of their children, but he knows what a great mother she is.