Bug biting skin of heartbreakingly small body (8)
I believe the answer is:
physique
'body' is the definition.
(I know that physique is a type of body)
'bug biting skin of heartbreakingly small' is the wordplay.
'bug' becomes 'pique' (I can't justify this - if you can you should believe this answer much more).
'biting' is an insertion indicator (some letters bite or swallow others).
'skin of' suggests removing the centre.
'small' becomes 's' (abbreviation - e.g. clothes size).
'heartbreakingly' with its centre taken out is 'hy'.
'hy'+'s'='hys'
'pique' placed around 'hys' is 'PHYSIQUE'.
Can you help me to learn more?
(Other definitions for physique that I've seen before include "Shape and size of a person's body" , "Form" , "Constitution of the human body" , "Person's build and muscular development" , "Bodily type, build, or constitution" .)