Your old skinny sweetheart (5)

I believe the answer is:

thine

'your old' is the definition.

'skinny sweetheart' is the wordplay.
'skinny' becomes 'thin' ('thin' can be similar in meaning to 'skinny').
'sweetheart' becomes 'e' (the heart/centre of 'sweet'**).
'thin'+'e'='THINE'

(Another definition for thine that I've seen is " Yours (archaic)".)

I've seen this clue in The Telegraph.

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