His Convenient Wife by Diana Hamilton

Cat is furious when her grandfather insists she consider a marriage of convenience to wealthy Italian businessman Aldo Patrucco. But then it’s love at first sight for Cat and lust at first sight for Aldo — so the wedding is on! Once in Italy, Cat plans for her new husband to fall in love with her — only it seems he’s returned to his mistress! Proudly announcing she’s leaving him, Cat discovers that, mistress or not, Aldo certainly has no intention of relinquishing his convenient wife…