etimología necesaria (cómo me entero de esto una noche de septiembre luego de 22 años de llamarme así)

Melanie: deriva del griego Melaina, cuyo significado es oscuridad, melancolía.
Y luego, la explicación mitológica (sin intención de traducir):

Melaina ("The Black One") is the under-earth or chthonic aspect of the Greek Great Goddess, said to bring nightmares. Different goddesses are called by Her name.

Aphrodite Melaenis represents a dark aspect of the goddess of love as Underworld deity, though some say She is called "Black" because love-making often takes place at night.

The Underworld goddess Melinoe was considered the daughter of Persephone (Kore) and Hades, Queen and King of the Underworld. She was called Chthonia, "Of the Lower World", a name also applied to Demeter. She was said to be half dark and half light (like Hel), from Her dark father Hades and Her mother who represented light. She walked the earth after dark bringing fear and night terrors. As Persephone is considered to be a form of Demeter as Death Goddess, so Melinoe should probably be seen as another Underworld aspect of the Greek Great Goddess.