What proof does Hazel discover of Malabar and Ben's affair as noted in the memoir, Wild Game: My Mother, Her Lover, and Me?

Charles' caretaker Hazel discovers proof of Malabar and Ben's affair in the back of the filing cabinet. Malabar kept a file folder of memorabilia from her affair with Ben that included napkins, tickets, and matchbooks from their trips together, as well as explicit photographs and a love letter from Ben.