Fairest of Them All by Teresa Medeiros

Who is the fairest bride of all?
Sir Austyn of Gavenmore abides beneath the shadow of an ancient Welsh curse. Given to fits of violent jealousy, the Gavenmore men are doomed to heartbreak by their inability to trust the women they love. Austyn fights his destiny until he comes face to face with Lady Holly of Tewksbury, the fairest damsel in all of England.
Weary of being revered only for her beauty, the mischievous Holly devises an elaborate ruse that unwittingly makes her a Gavenmore bride. Thus begins a dangerous masquerade in which Holly and Austyn must learn that even the most irrevocable of curses can be broken by the blessing of true love.

Book 3 in the Once Upon a Time Series, which includes Charming the Prince, The Bride and the Beast, and Fairest of Them All