Love is a subtle theme in Franny and Zooey; there is no discussion of it explicitly aside from the narrator's cryptic claim that his story "Zooey" is in fact a love story rather than a mystical story. The theme does come cross implicitly in Zooey and Franny's discussion of spirituality. The text's implicit conclusion seems to be that every person, no matter how materialistic or petty or shallow they are, deserves love. This is one interpretation of the way in which "Zooey" is a love story. It is by no means the only one.
Franny and Zooey argues that family love is the strongest kind of love there is.
Though Buddy introduces his story as a love story, rather than a mystical story, it is in fact just the opposite. His introduction is intentionally misleading.