The conflict is the unrequited love of the boy. Of course his mother should love him but she cannot. Bowen used detailed descriptions of the natural world, in the park, to mirror the relationship between the mother and child:
“Poplars stood up like delicate green brooms; diaphanous willows whose weeping was not shocking quivered over the lake. May sun spattered gold through the breezy trees; the tulips though falling open were still gay; three girls in a long boat shot under the bridge.”
The weeping of the willows was not shocking represents how the mother is untouched by her son's emotions. The two additional sentences "May sun splattered..." above show how the world goes on, even when one person is suffering intensely. This is Bowen's understanding of human suffering. It is spiritual because we do it alone. Always when one suffers, it is alone.
Of course, the reader can understand why the child is sad. His father died. And his mother is not kind or understanding of him.
The climax is when climbs over the fence and goes after the duck. Here the reader thinks he will meet with danger. He doesn't however. Instead, he meets the woman on the park bench and how her simple attention to him gives him hope. At the end of the story we can see that Fredrick has fond memories of when he tried to catch the duck. Even though he cannot remember the woman. Was she real?, the reader might ask. Because if she were real why didn't Fredrick's mother enquire about the apple ? Like "where did you get that apple ?"
The title of the story comes from Tennyson. It is about divine sorrow. It is also about not understanding our feelings. In the story the woman on the bench realizes that he knows something, more than he should. Here, Bowen is referring to a spiritual kind of "knowing". The child is aware of his sorrow and is grieving, even though his mother is unaware. After the woman on the bench reflected back to him his own self worth, he was better.
This is the resolution.