It's safe to say that Hero and Leander are in love. Hero chooses to break her vow of chastity for the guy, and Leander risks his life every night by swimming across the Hellespont just to be with her. From what we can tell, their nights together were perfect, blissful, and full of lovin'. But in the end, their love is the precise thing that destroys them both. It causes Leander to make the highly questionable decision of swimming across the Hellespont in a storm, and it drives Hero into suicidal despair when she finds his body. However sweet it was while it lasted, love ultimately turns into a force of destruction in this tragic tale.
When Leander drowns in the stormy waters of the Hellespont, it doesn't just mean the death of him as a human being; it also means the death of the passionate affair he has with Hero. The loss of Leander's love is just too much for the girl. And ironically, she decides that the only way to be with her lover is to join him in death—the very thing that took him away.