Can you help me remember this book title?

I read a historical romance a couple of years ago that keeps coming to mind but I can’t remember the author or title.

What I recall is that the heroine I think works for the hero. He starts falling for her and they’re kind of sneaking around. One time they’re in a room of his home and look through the window or glass door and she his younger sister kissing a member of the household staff. The hero is furious and wants to storm out and confront them and the heroine tries to remind him that he’s being a hypocrite.

Does this ring a bell for anyone? I read a lot of Lorraine Heath, Elizabeth Hoyt, Lisa and Kleypas.