This Could Change Everything - Jill Mansell

One little mistake and nothing will ever be the same again! On the one hand, if Essie hadn't written that letter - the one that only her best friend was meant to see - then she'd still be living like an actual proper grown-up, tucked up with Paul in his picture-perfect cottage, maybe even planning their wedding... On the other hand (if her true feelings hadn't accidentally taken the internet by storm, that is) she wouldn't have moved into the attic flat on the square. She would never have met Conor. Or got to know Lucas. And she wouldn't have found herself falling in love with someone she really, really shouldn't fall in love with.