Regency romance with a widowed/divorced Hero(marquess/duke)

Hi, I have been looking for this book for years now. It is a regency romance

The plot: The hero is a duke or marquess(not sure) who is closed off to the herione(Catherine?) because his ex wife (late wife?) hurt and betrayed him but he eventually falls in love with heroine and happily ever after.

Scenes I remember:
The first scene I remember is when the hero meets the heroine in a rather rude encounter, I think it was on the road (now I hope I am not mixing up two books but I think it turns out she is his ward and she has to live with him for a time)

The climax is when something happens towards the end that makes the herione take off/run away from hero's home on a horse and gets thrown and almost dies and the hero has to bring her back