Why does Sonny leave Isabel's family's home while the narrator is in the military in "Sonny's Blues?"
While Sonny is with Isabel's family, he certainly does take advantage of the opportunity to practice on the piano and listen to music. This becomes his life. The narrator adds that Sonny is not rude nor unpleasant. Still there is a distance between Sonny and Isabel's family. He lives and moves about as if he is in a slightly different world than they are. The narrator, his brother, describes it:
They fed him and he ate, he washed himself, he walked in and out of their door; he certainly wasn't nasty or unpleasant or rude, Sonny wasn't any of those things; but it was as though he were all wrapped up in some cloud, some fire, some vision all his own; and there wasn't any way to reach him.
Sonny had been missing school. When the school sent letters to Isabel's house, Sonny tore them up. But one got past him and Isabel's mother confronted Sonny about this, screaming about how their family had made sacrifices for him. (Sonny had been spending time in Greenwich Village with some musicians and at a white girl's apartment. When Isabel confronts him, she breaks down and cries as well. Even though she tried to be gentle with Sonny about her disappointment, he was going to take this very hard. The narrator notes that they had broken through Sonny's "cloud" and affected him personally. To know that the one thing that gave him life and hope (playing music) had been a burden to this family was enough to make Sonny consider leaving. After a few days, Sonny takes his records and leaves. He could not bear to live in a home where he was such a burden. The narrator adds that Sonny realized they undertook this burden for him (narrator) and not necessarily for Sonny himself:
For he also had to see that his presence, that music, which was life or death to him, had been torture for them and that they had endured it, not at all for his sake, but only for mine.