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

Santina was Davide Segre's lover. She is described as an unattractive, older prostitute, who takes Davide in. It isn't clear why Davide is initially attracted to Santina, but over time, he begins to rely on her company and perhaps, he even loves her. After Santina's murder, Davide takes over the apartment and lives there for the rest of his life.