Married Lovers by Jackie Collins

Second Hand 

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.