Glaucus and Scylla. To find out more about Scylla and her love for Glaucus, see this Wikipedia article: link; for information about the image: image source.
In a story told in Ovid's Metamorphoses, Scylla was a nymph and Glaucus (once a fisherman, now a god of the sea) fell in love with her. He went to the witch Circe to ask for a love potion, whereupon Circe fell in love with Glaucus. What a love triangle! Circe was insanely jealous of Scylla and poured a poison into the water where Scylla bathed. As soon as Scylla entered the water, she was transformed into a savage monster with six heads and twelve feet, along with the heads of wolves that emerged from his waist. She went on to be known as one of the most savage sea monsters, paired with the whirlpool Charybdis. Meanwhile, in today's image, you see Scylla in her happier days as a lovely nymph!