The Duke of Disorder by Anna St. Claire

He saves her from a runaway horse. Too late, she realizes her hero is the man she left years ago for another.

Lucas Pemberton, the fourth Duke of Dorman, enjoys the freedom life affords him and has no plans for marriage, having experienced the fickle nature of women years ago. On the way home, a woman’s piercing scream and an out-of-control horse grab his attention. He rescues her, only to discover that she is the woman who had spurned his affections years ago in favor of another.
Unexpectedly, he becomes guardian to two young women—a forgotten promise made long ago. A confirmed bachelor, Lucas finds himself wholly unprepared for the challenges his wards create and force him to seek a solution.
Newly widowed, Lady Harriett Dudley flees her dead husband’s home, and vows to never relinquish her freedom to any man. Distracted by threats from his family, she is almost killed when something spooks her horse, only to be saved by the man who had professed his affection the very day her father betrothed her to another.

Did she owe him an explanation? Would he understand? Could forgiveness revive a long-ago courtship and give them an opportunity to experience everlasting happiness?