Paramour slightly off-centre? (1,3,2,3,4)
I believe the answer is:
a bit on the side
'paramour' is the definition.
(both can mean a lover)
'slightly off-centre?' is the wordplay.
'slightly' becomes 'abit' (I've seen this before).
'off-centre?' becomes 'ontheside' (something on the side is not central).
'abit'+'ontheside'='A BIT ON THE SIDE'
(Other definitions for a bit on the side that I've seen before include "secret of a cheat?" , "Extramarital partner" , "illicit lover" , "Mistress?" , "as sauce on a plate?" .)