Yes, I loved this one when I read it on YA, and it still enthralls my mind.
Sweet William reminds me of an old song called Barbra Allen, where she sings "Sweet William died for me today, I'll die for him tomorrow"
On William's grave grew a red red rose,
On Barbra's grew a green briar.
They grew and grew to the old church tower,
Til they could grow no higher.
And there they tied in a true love knot,
The rosebush and the briar.