Who is Eunice from Tides of War: A Novel of Alcibiades and the Peloponnesian War and what is their importance?

Eunice is the mother of Polemides' children, as well as his companion. The couple never officially marries, and Eunice is considered his "camp wife". A jealous and vindictive woman, Eunice poisons polemides second wife, sleeps with Alcibiades, and plays a large part in his arrest for murder. Each of these acts is an act of revenge, although, Eunice never stops loving him..... nor does he never stop caring for her.