What does wear the willow mean?

Answer 1

"wearing the willow" was a - usually metaphorical - sign that you were mourning the loss of a lover - most particularly it was used of a maiden who has been abandoned before marriage, like, for example, Queen Dido who was abandoned by Aeneas, and is referred to in Shakespeare's play "The Merchant of Venice":

In such a night

Stood Dido with a willow in her hand

Upon the wild sea banks and waft her love

To come again to Carthage."

There's an early 17th century source, giving a Ballad called "The Willow Tree", which is a dialogue between two shepherds, one of whom explains:

"Yet Phillis still I pine for thee

And still must wear the willow tree."

showing that it was used for forsaken men as well as women.

This tradition is also mentioned in Maddy Prior's song, "All around my hat, I will wear the green willow," where (IIRC) it is being used ironically.