Five alluring literary love triangles

At B&N Reads Tara Sonin tagged five favorite literary love triangles, including:
The Mists of Avalon, by Marion Zimmer Bradley

Possibly the ultimate fantasy love triangle in the ultimate fantasy novel: the story of Arthur’s rise to the throne of Camelot, told by the women surrounding him from his priestess half-sister Morgaine to his Queen Gwenhwyfar, who had a forbidden love for Lancelet, one