Another Kind of Cowboy by Susan Juby

From the back of the book:
For Alex Ford, dressage is an oasis. In the stable, he can slip into his riding pants, shed the macho cowboy image, and feel like himself for a change. For Cleo O'Shea, dressage is a fresh start. She's got a new boarding school, absentee parents, and, best of all,not one to remember he past. When their paths collide, Alex doesn't want to have anything to do with the privileged, overbearing girl, not least because she doesn't seem to get how lucky she is to be riding horses all day. But when Alex can't shake Cleo, he soon realizes she might be the only one who understands him. After all, keeping a secret is as tough as getting a orse to dance. Sometimes you need a little help.