Saudade

Saudade (Portuguese): The feeling of longing for someone that you love
and is lost. Another linguist describes it as a "vague and constant
desire for something that does not and probably cannot exist."

It's interesting that saudade accommodates in one word the haunting
desire for a lost love, or for an imaginary, impossible,
never-to-be-experienced love. Whether the object has been lost or will
never exist, it feels the same to the seeker, and leaves her in the
same place: She has a desire with no future. Saudade doesn't
distinguish between a ghost, and a fantasy. Nor do our broken hearts,
much of the time.