The mythology of Celtic fairies shows several instances of fairies taking on mortal lovers. The following reads an excerpt from The Encyclopedia of Celtic Mythology and Folklore:

“fairy lover… Irish, Scottish, and Breton folkloric figure. Many stories of FAIRYLAND centered on this ravishingly beautiful woman—for it was almost always a woman—who stole away the most brilliant poet or the most handsome man from this world and made him her lover. Not that it required much work on the fairy woman;s part, for these gorgeous beings made the most beautiful mortal woman seem coarse and unattractive. The fairy mistress called to her chosen mate through dreams that haunted him until he sought her out, living on her charmed ISLAND in the western sea or beneath some ancient mound. Once he tasted her charms, he rarely attempted to leave her, since she was not only magnificent to look upon but was utterly wanton. Because time passed differently in fairyland than in our world, a single night with the fairy mistress crept by pleasantly while centuries slipped away on this side of the veil. When, as occasionally happened, the human lover grew homesick, he returned to find his home dissolved in the mists of time and usually lost his fairy lover to boot….Fairies were notoriously fickle, so sometimes a fairy woman discarded her human husband and sent him unceremoniously back into this world. 

Rarely could such a man recover to lead a normal life. More commonly, he pined away and died soon after his return, longing for the beauties he saw in fairyland. Occasionally…he survived and finally returned to his fairy lover, to live happily in the Otherworld thereafter. …Occasionally fairy kings stole human maidens away, often on their wedding day; in addition, there are tales in Scotland and Ireland of male fairies who seduced young women. But it is much more common to find the fairy lover in female form.”