Holden cries before he leaves the apartment because his sister has given him her Christmas money. Holden needs money and Phoebe, his little sister, offers him the money she has saved to buy Christmas gifts, he is so touched by her generosity that he cries.
Holden is home for only a brief time, but during this time he is happy. Happy to be with his sister, Phoebe, whom he trusts and loves. She loves Holden unconditionally, no matter what he has done. For a brief time, Holden is a whole person, sharing fun experiences with his sister in the comfort and security of his home.
Leaving his home again, his sister, and all the comfort that it provides, in addition to his sister's generosity, makes Holden feel very sad, he cries.
His crying, to me suggests, that Holden really belongs at home, he should not be running away from his family, they are the only people who can actually help him.
Adolescence is ironically an unhappy period of life for many boys and girls. This unhappiness is ironic because they are young and most of them have no serious health problems or real-world problems--yet! Holden is crying when he leaves his home at the end of chapter 23 because he has been crying internally since the beginning of the novel. His main characteristic is that he is unhappy--and this is probably why so many readers, especially young readers, can relate to him. The author J. D. Salinger was probably unhappy as a teenager himself. Salinger was really remembering his own adolescence in the character he created. Holden is obviously looking for something throughout the entire book. He is unhappy because he feels lonely and because he has a bad opinion of himself. Many adolescents feel the same way, but Holden is especially sensitive and probably suffers more. Why is he unhappy? Who knows? Adolescence is just an unhappy time. It is a transition from childhood to adulthood. The adolescent doesn't understand the changes that are taking place inside him or her. They look at themselves in mirrors a lot, wondering who they are and what the future holds in store for them. Holden believes that he can find happiness outside himself, and he is continually disappointed with everyone he looks up. The only exception is his little sister Phoebe. She makes him cry because she loves him but is too young to understand him. All she can do is give him the little bit of money she has saved up for Christmas. She breaks the dam that has been holding back her big brother's emotions from the time he was ostracized by his fencing team and expelled from yet another private school. Unhappy people naturally see the bad side of the external world, whereas if they were happy the world would look entirely different. There is an old saying that covers this truth: "Laugh and the world laughs with you. Cry and you cry all alone." Holden is not too much different from Pip in Charles Dickens' novel Great Expectations. Pip was looking for something in the external world which the external world couldn't provide. He finally realized that he had to settle for a lot less than he had expected. Many philosophers have offered virtually the same advice: Don't look for happiness outside yourself. Happiness comes from within.
Holden cries as he leaves his house at the end of chapter 23 because Phoebe had given him money, despite saving it all year in order to buy christmas presents for everyone. He is touched by her act and it leads to him crying as he thinks about just how much he loves his sister/