Her Secret Cowboy (Harlequin American Romance Series #1486)

The Cowboy And The Preacher's Daughter 

Years ago, Will Cash wasn't interested in being a dad. So Marsha Bugler left town to raise her baby alone. But when her father's health begins to fail, she realizes she needs to return to Arizona—and introduce Will to his boy. Marsha is nervous to face Will not only because she lied, but because she's never stopped thinking about her cowboy crush. 

Will is shocked to discover he has a son. And he can hardly believe the changes in Marsha. She's strong, sexy and a Ph.D. while Will's still a part-time cowboy living in a bunkhouse with his brothers. What does he have to offer her and his teenage son? Will has a lot to prove if he's going to get what he wants—the family he never knew he had.