I’m trying to find an illustrated storybook set in a medieval fantasy setting. It may be a children’s book but the story and theme are very morbid. I think the book was published in the late 1970s or early 1980s. The illustration style is drawn in detail and colored, possibly watercolor.

The protagonist is a young hero, possibly a prince, who is betrayed or abandoned by the woman he loves. Perhaps their courtship was called off after he performed a great deed or quest for her father?

He somehow ends up heartbroken and dying on a small island in the sea.

He stays alive by sucking the salt and tears from the tattered and faded blue or black cloak that he wears. Eventually the cloak becomes magically imbued with a toxic curse and is blown on the wind to the kingdom where his former lover lives.There it spreads a deadly plague, possibly the Black Death. I vaguely recall an image of the woman dying from the plague with birds strapped to her feet (an ineffective cure meant to ward off the plague)

Does this ring a bell for anyone?