Cruel Romeo's jilted Mary Jane (4)
I believe the answer is:
'mary jane' is the definition.
(slang for marijuana)
'cruel romeo's jilted' is the wordplay.
'cruel' becomes 'harsh' ('harsh' can be a synonym of 'cruel').
'romeo' becomes 'r' (phonetic alphabet: alpha, bravo, charlie etc.).
'jilted' is a deletion indicator.
'harsh' with 'r' taken away is 'HASH'.
(Other definitions for hash that I've seen before include "What signifies a number" , "Mess; meat/potato dish" , "Meat dish; mess, jumble" , "Keypad symbol" , "Stew - key" .)