Metamorphoses Book 9: Byblis
Byblis fell in love with her brother, Caunus, and she tried to fight the feeling because she knew that incest was wrong. But soon her feelings got the better of her and so she wrote him a letter telling him how she felt and hoping that he felt the same. He was revolted by the idea, and when Byblis wouldn't give up her pursuit, he left home. He went to found a new city, and when she tried to follow him, she couldn't find him. She sat down by a stream a cried for so long that a wood nymph turned her into a spring.