The devil in the saddle / Julia London.

Enhanced descriptions from Syndetics:

No one cheats on a Prince and gets away with it. And Hallie--Texas socialite, would-be ballerina, and the only daughter of Cimarron County's renowned Prince family--is ready to give her two-timing fianc a piece of her mind. But fate plants hot, sexy ranch hand and ex-Army Ranger Rafael Fontana quite literally in her way. Her childhood friend is all grown up. He's sexy, he's handsome, and, suddenly, after all these years, Hallie is taking notice. Rafe has been in love with Hallie since they were kids, but he was always the help--and she was glamorous and popular, seemingly off-limits to a lowly cowboy. But now he's back at Three Rivers Ranch to help his family, and Hallie is there too--and she needs his support. Of course, Rafe agrees, but soon, long-buried feelings boil to the surface, and the desire between them is hot and palpable and undeniable. Rafe realizes he wants Hallie for keeps...he just has to convince her to give true love another shot.