Libertine group originally haunting a former capital (8)
I believe the answer is:
lothario
'libertine' is the definition.
(both can mean a womaniser)
'group originally haunting a former capital' is the wordplay.
'group' becomes 'lot'.
'originally' indicates taking the first letters.
'former capital' becomes 'Rio' (Rio de Janeiro, former capital of Brazil).
The first letter of 'haunting' is 'h'.
'lot'+'h'+'a'+'rio'='LOTHARIO'
(Other definitions for lothario that I've seen before include "Successful womaniser" , "Heartbreaker" , "A literary libertine or womaniser" , "Libertine - ol' hot air (anag)" , "Womaniser, philanderer" .)