You Deserve Each Other by Sarah Hogle

Naomi Westfield has the perfect fiancé: Nicholas Rose holds doors open for her, remembers her restaurant orders, and comes from the kind of upstanding society family any bride would love to be a part of. They never fight. They're preparing for their lavish wedding that's three months away. And she is miserably and utterly sick of him.

Naomi wants out, but there's a catch: whoever ends the engagement will have to foot the nonrefundable wedding bill. When Naomi discovers that Nicholas, too, has been feigning contentment, the two of them go head-to-head in a battle of pranks, sabotage, and all-out emotional warfare.

But with the countdown looming to the wedding that may or may not come to pass, Naomi finds her resolve slipping. Because now that they have nothing to lose, they're finally being themselves--and having fun with the last person they expect: each other.