French sociologist Pierre Bourdieu wrote a book on single adults in the region of Bearn, southern France. In Spain it was published with the title "El baile de los solteros". I do not know if it is published in English or not.
I'm late to this but Going Solo by Eric Klinenberg is an interesting study of adults who live alone. At the end he makes some observations and suggestions about how communities could better incorporate single individuals.