Symbolism, Imagery, Allegory
At the end of Rabbit, Run, Rabbit decides that, because Ruth and Janice both have parents that can help her, he can absolve himself of responsibility for them. But Nelson is another matter. Nelson has become the tool by which Rabbit can weigh all his other actions. If Nelson is doing ok, then Rabbit must be doing the right thing. Regardless of what he does, how his actions might affect Nelson will be a major consideration in the future.