How does the theme of obsession arise within the story about Kunicki?

The theme of obsession arises within Kunicki's story when he becomes completely fixated on the truth of his wife and son's three-day absence. He believes that his wife is lying about getting lost and spending nights in meadows and all the rest. As his obsession with the subject grows, his inability to let the matter go grows as well, until he can no longer remain in his marriage because the matter bothers him so deeply.