Left in Santiago, desperately yearning for the past (9)
I believe the answer is:
nostalgia
'yearning for the past' is the definition.
(I've seen this before)
'left in santiago desperately' is the wordplay.
'left' becomes 'l' (common abbreviation).
'in' is an insertion indicator.
'desperately' indicates an anagram.
'santiago' with letters rearranged gives 'nostagia'.
'l' placed into 'nostagia' is 'NOSTALGIA'.
(Other definitions for nostalgia that I've seen before include "A longing for past times" , "Sentimental feeling of analogist" , "Fond memories" , "That may bring on homesickness" , "Fond remembrance" .)