The Mating Intent (Book 4.5 in the Werewolves of Montana) by Bonnie Vanak
Twenty-five years ago, Gabriel Sanders took Sienna Bennett's virginity in a night filled with fiery passion. For breaking her vow of celibacy, Sienna was severely punished by the Fae king. If she surrenders to Gabriel's sensual allure this time, Sienna faces banishment from her people forever.
Gabriel burns for Sienna and has never forgotten the taste of her mouth, nor the exquisite pleasure they shared in his bed. Only Sienna can satisfy his intense need to mate. He desperately needs her dark Elven magick to fight a deadly curse that is killing shifters and destroying his territory. Gabriel must convince the pretty Elf to bond with him to defeat the dark enchantment before it destroys the Everglades for good.