What revelation finally reconnects the two sisters, Haven and Ashley, in the story, That Summer?

Haven is angry with Ashley for breaking up with Sumner, who she believes to be the ideal boyfriend. When Ashley finally reveals the truth.... Sumner hadn't been the perfect boyfriend that Haven had believed him to be; his cheating on Ashley is what split them up. This news changes things between Haven and her sister, and Haven realizes that Ashley had been devastated both by Sumner's behavior and her father's leaving. Between the two, she had almost lost her faith in men. Haven finally understands that her family will always be her family, and takes strength from it.