Two exes. One pact.Could this holiday change everything?'One of my favourite authors' Colleen Hoover, It Ends With Us'The master of witty repartee' Daily Mail-------------------------------------------------------------------------------------------------------------------------Harriet and Wyn are the perfect couple - they go together like bread and butter, gin and tonic, Blake Lively and Ryan Reynolds. Except, now they don't.They broke up six months ago.And they still haven't told anyone.Which ...