Fitting end of affair in bonding with heartless organisation (6,2)
I believe the answer is:
trying on
'fitting' is the definition.
('trying on' can be a synonym of 'fitting')
'end of affair in bonding with heartless organisation' is the wordplay.
'end of' says to take the final letters.
'in' means one lot of letters goes inside another.
'bonding with' becomes 'tying' ('tie' can be a synonym of 'bond with').
'heartless' says to hollow out the word (remove centre letters).
'organisation' with its centre removed is 'on'.
The last letter of 'affair' is 'r'.
'r' going within 'tying' is 'trying'.
'trying'+'on'='TRYING ON'
(Other definitions for trying on that I've seen before include "checking suitability of outfit" , "Tiresome" .)