whether or not these sacrifices have had a positive or negative effect

It is not until Jimmy faces his own personal setback—dislocating his shoulder and being forced to quit the swim team—that he and Lisa become close again. The siblings mutually help each other regain a sense of stability after experiencing great hardship. His fate at the end of the novel is not revealed. What sacrifices that Jimmy makes help him become closer to his sister which seems like a good thing. I think that sacrifices are usually a trade off. Sacrifice is given for some kind of gain: life tends to be like that. You will need to scan the text for your quotes.