From the Start by Cheryl Etchison

The Rangers of the 1st/75th fight hard, train hard and play hard. They are physically strong and mentally tough, disciplined and courageous. But all their military training hasn't prepared them for falling in love.

For many women, Ranger Battalion Surgeon Michael MacGregor is the ideal man. He's far better than average looking, a generous tipper, not to mention an officer and a doctor. So when he encounters a woman resistant to his charms, he finds himself... intrigued.

Kacie Morgan has had her fill of arrogant military men since the last one left her with a shattered heart and one heck of a career rut. Now, with her prestigious fellowship starting in the fall, all she has to do is survive the summer--and her little sister's wedding. 

When an ill-fitting bridesmaid dress has Kacie wanting to temporarily shake things up in her carefully planned life, she knows just the man to call. They agree to a no-strings, summer fling, although it isn't long before Michael wants Kacie for forever.

But to win her heart, he'll have to confront the nightmares from his past if they're to have any chance at a future.