My best friend's brother - Laura E. Kennedy

Erica can barely believe it when she falls for Jake - her best friend Sally's brother - and discovers he feels exactly the same. She feels a world of opportunity ahead for the best summer ever hanging out with Jake and Sally. But then Sally discovers that her and Jake's beloved father is having an affair. Sally swears Erica to secrecy, especially from telling Jake, while she tries to find out exactly what her father is up to. The secret grows until one night Erica realises that Sally could be in trouble and she must betray her trust - and risk losing Jake.