Overall, I really liked this story, and I didn't mind the ending - fatherhood/family life was the main theme of the story, after all. But, as someone else pointed out above, it seemed like Tim Pratt sort of wrote himself into a corner with the mother. Basically, he needed her to have the affair to make the parallelism about the desire for adventure, and chosing family over it, but he also didn't want to keep her around - or otherwise the son would be abandoning two parents, one who had nothing to do with the axe, and that would change the meaning of that scene - so he had to kill her off in a totally unrelated way immediately after. Like Scattercat, my first inclination was to think she was somehow being manipulated by the axe, but the story never acknowledged that possiblity. So, either the axe did it but this was too subtle, or it was just a total coincidence and thus broke the internal believability of the story.
This isn't a big enough problem to seriously diminish my enjoyment of the story, but it felt like a misstep, and I think Pratt is a good enough writer to have avoided it.