The Girl Before Eve by Lisa J. Hobman

Lily and Adam have been best friends since the dawn of time… Okay since primary school to be exact. They have always been accepted as a double act…a package deal…and they like it that way. Until one fateful day in the summer they are 18, when Lily makes a terrible discovery–she is head over heels in love. With Adam. Lily’s unrequited feelings are hard to deal with as it is but this is further compounded when she inadvertently introduces Adam to the love of his life.