Who is Santina from History: A Novel and what is their importance?

Davide Segre's lover, Santina, is an unattractive, older prostitute who takes him in and is good to him. It is not clear why Davide is attracted to Santina unless she reminds him of his mother. He begins to rely on her company and perhaps, even loves her. When she is murdered, Davide takes over her apartment and lives there until his death.