God Rest Ye Merry Spinster by Rebecca Connolly

Christmas is here, and Elinor Asheley’s entire family has gathered at their country estate to celebrate. But when her arch nemesis arrives at the estate by chance, warm wishes and the holiday spirit are the last things on her mind. Elinor is determined to protect her family from him no matter how changed he claims to be.
When the winter weather strands Hugh Sterling at the estate of the woman who hates him most in the world, his only wish is to escape the place unscathed. He is not the man he once was, and he will do everything he can to prove that to Elinor. But nothing can prepare him for the changes that spending his holiday with her will bring.