Unforgiven question

Hello!
I read a historical romance novel a few months back and I can’t remember the name. The plot was something along the lines of the hero and heroine being invited to attend a 7 day (maybe less?) event at a lady’s (side character) house. The reason why she (the side character) decided to have much a long event is because she suspected that her husband fell out of love with her and she tried to regain his love and have him look at her again. Turns out at the end that wasn’t the case and the husband is beyond in love with her. The hero and heroine wear their masks the entire time (or something like that) and the hero confesses that he likes the heroine to the lady of the house. The lady (side character) of the house was somewhat related to him (by blood or by in law, I’m not sure?). I think the hero either didn’t recognize the heroine or couldn’t because of the mask but the heroine knew who the hero was. Does anyone know the name of this book? It’s a historical romance novel!