Libertine reluctant to take fresh air; nothing more (8)
I believe the answer is:
lothario
'libertine' is the definition.
(both can mean a womaniser)
'reluctant to take fresh air nothing more' is the wordplay.
'reluctant' becomes 'loth' (if you are loth to do something you are reluctant).
'to take' says to put letters next to each other.
'fresh' is an anagram indicator (a fresh re-ordering of the letters).
'nothing more' becomes 'O' (resembles 0).
'air' with letters rearranged gives 'ari'.
'loth'+'ari'+'o'='LOTHARIO'
(Other definitions for lothario that I've seen before include "Don Juan-type character" , "A literary libertine or womaniser" , "A Gay libertine" , "Seducer, rake" , "Womaniser, philanderer" .)