Seer of Sevenwaters by Juliet Marillier

Prior to making her final pledge as a druid, the young seer Sibeal visits the island of Inis Eala, where the Sight leads her to Felix, a survivor of a Norse shipwreck who has no memory of his past. As the island's healers struggle to keep Felix alive, he and Sibeal form a natural bond. But Sibeal's vocation is her true calling, and she must choose between the two things that tug at her soul-her spirituality and a chance at love...