This gives me masses of goosebumps and chills, especially at the end when Eluveitie's Chrigel Glanzmann (a guest singer here) growls the words apparently from an ancient text in Welsh. Gwydion is a magician, hero and trickster of Welsh mythology.
I heard this a long time ago, on the radio while driving. It somehow circumvents my aversion to romanticism about relationships. It has a very Interstellar (movie) mood.