Married lovers / Jackie Collins.

Enhanced descriptions from Syndetics:

Three high-powered Hollywood couples, two hot affairs, one underage Russian ex-hooker, a passionate murder-and the players' lives are changed forever. Cameron Paradise , a stunningly beautiful twenty-four-year-old personal trainer, flees Hawaii and her champion-surfer husband, Gregg , in the middle of one of his abusive tirades and makes her way to L.A. Tall, blond, with a body to die for, it doesn't take Cameron long to find a job at an exclusive private fitness club where she encounters LA's most important players. She has plans to open her own studio one day, and while every man she meets comes on to her, she is more focused on saving money and working hard than getting caught up in the L.A. scene of wild parties and recreational drugs.Until she meets Ryan Lambert, an extremely successful independent movie producer. Ryan is married to overly privileged Mandy Lambert , the daughter of Hamilton J. Heckerling , a Hollywood power-player son-of-a-bitch mogul. Ryan has never cheated on his demanding Hollywood Princess wife, but when he meets Cameron, all bets are off, especially since she's seeing his best friend Don Verona , the devastatingly attractive talk-show host and legendary player.In her latest sizzling blockbuster, internationally bestselling author Jackie Collins explores what happens when lust and desire collide with marriage and power-and the results lead to murder.