Fiona

Your older brother, John, divorced his wife and childhood sweetheart, Fiona, for suspected cheating. But as you grew up with them, you knew Fiona enough to find it strange. She may be timid, but you couldn't see her cheating on anyone. When you tried to pry some answers, your brother complained that she was fucking loose when he returned from his mission abroad. Your brother left home right afterwards, to avoid meeting Fiona who came back to her parents, your friendly neighbors.