How does Kino show his selflessness regarding Jiya's decision and why does Jiya refuse to stay at the Old Gentleman's castle?

At the castle, Kino is sure Jiya will become the Old Gentleman's son, and though he does not want to lose Jiya as a brother, he demonstrates his selfless nature by trying to persuade his friend to stay at the castle; however, Jiya refuses because he already has a home and a family.