Historical romance where hero locks heroine in a dungeon

[Meredith]

I am looking for a book I read a while ago. I thought it was Lady Gallant, but I reread that book and turns out it is not what I was looking for but very similar. The hero at one point locks the heroine in a dungeon/tower for revenge against her (I can't remember what he thought she did). I remember when she gets out of the dungeon she falls from a horse and it turned out she was pregnant the whole time she was locked up without the hero knowing. There's also some cheating that goes on from both the hero and the heroine. I know she sleeps with some military leader (I think that's what he is) possibly in order to pardon her husband somehow. And he sleeps with another women to get revenge on her during the book as well. Those are the only real clues I can think of at the moment.

[Kris]

Meredith, around what year did you read this book? A range of years is fine. I find "a while ago" means different things in this large group.

[Meredith]

I read it about 2 years ago.