Blame It on the Rodeo (Harlequin American Romance Series #1487)

A Secret The Size Of Texas 

Veterinarian Lexi Lawson has her hands full—and not just when she's delivering foals at the Langtry family's ranch. Working there forces Lexi to confront Shane Langtry, the man who broke her heart. True, he seems different now—more generous, more grounded. But Lexi isn't fooled: Shane lives for rodeo competition and nothing else. Besides, after what he did to her, there's no way she'd take him back. 

Long ago, when they were in love, Lexi hid a terrible secret from Shane—one she planned to keep forever. But when he learns the truth, she's forced to choose between the past she left behind…and the future they might still find together.