Matthew's affair provides the catalyst for Susan's tragic descent into madness and suicide. Susan always thought she'd led the perfect middle-class life: a nice house, children, and a hard-working, loving husband. Once she discovers the sordid little details of her husband's infidelities, however, she realizes that it's all just a sham. What makes things worse is that with the children away at school, Susan has no outlet for her increasingly troubled emotions. It's as if she's been abandoned by everyone all of a sudden. Since she got married to Matthew, Susan's whole identity has been bound up with her family. With her children at boarding school and her husband cheating on her, Susan no longer feels like a mother or a wife. She doesn't know quite who she is anymore, and the consequences of this loss of identity are tragic.