What gets wrecked for Dexter?
It is his dream of her that is wrecked, not being able to have her. Even after Judy rebuffs Dexter half way into the story, dating other men, the narrator still says about him: “No disillusion as to the world in which she had grown up could cure his illusion as to her desirability.” Years later, after the war, however, that is just what happens: his illusion is destroyed. He hears that she has married and that her husband mistreats her, she stays home with her kids, and that “she used to be a pretty girl.” This information wrecks his dreams of her: he could live his dream of her even if he didn’t have her, but to have the dream of her beauty destroyed was devastating.
Dexter's dreams are "wrecked". He had an idea of what wealth, opportunity , and Judy's love would be like, and it was all a let down. His posturing in expensive clothes when he goes back to his hometown causes him to lose respect. He endures Judy's treatment towards him. In the end, he has lost his dream.