Retiring sort is an inspiration when embracing love (5)
I believe the answer is:
mouse
'retiring sort' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'an inspiration when embracing love' is the wordplay.
'an inspiration' becomes 'mus' (I am not sure about this - if you are sure you should believe this answer much more).
'when' becomes 'e' (I've seen this in other clues).
'embracing' means one lot of letters goes inside another.
'love' becomes 'o' (love means zero in tennis).
'mus'+'e'='muse'
'muse' enclosing 'o' is 'MOUSE'.
'is' acts as a link.
Can you help me to learn more?
(Other definitions for mouse that I've seen before include "shy and timid type" , "Computer accessory" , "retiring person" , "PC device" , "Timid fellow" .)