Poet's very soft-hearted darling (6)
I believe the answer is:
poppet
'darling' is the definition.
(I've seen this before)
'poet's very soft-hearted' is the wordplay.
'poet's very' becomes 'popp' (I can't justify this - if you can you should give a lot more credence to this answer).
'soft' becomes 'cretin' (I've seen this before).
'hearted' means to look at the middle letters.
The middle letters of 'cretin' are 'et'.
'popp'+'et'='POPPET'
Can you help me to learn more?
(Other definitions for poppet that I've seen before include "Sweet little darling" , "Term of affection for a child or sweetheart" , "adorable child" , "dear" , "Term of endearment" .)