Fling with fellow in a travelling show (6)
I believe the answer is:
affair
'fling' is the definition.
(I've seen this before)
'fellow in a travelling show' is the wordplay.
'fellow' becomes 'f' (abbreviation - of a society etc.).
'in' indicates putting letters inside.
'travelling show' becomes 'fair' (as in a fun fair).
'a'+'fair'='afair'
'f' inserted into 'afair' is 'AFFAIR'.
'with' is the link.
(Other definitions for affair that I've seen before include "Liaison or intrigue" , "Romantic relationship, perhaps illicit" , "Social event or sexual relationship" , "Secret sexual relationship" , "Happening" .)