Kisses Boris bottling up torment (6)
I believe the answer is:
obsess
'torment' is the definition.
(thesaurus)
'kisses boris bottling up' is the wordplay.
'bottling' says the answer is hidden in the clue (I've seen 'bottles' mean this (bottling is a kind of containing)).
'up' is a reversal indicator (in down clue: letters go upwards).
'ssesbo' is hidden in the letters of 'kisses boris'.
'ssesbo' written backwards gives 'OBSESS'.
(Other definitions for obsess that I've seen before include "Think only" , "Occupy the thoughts persistently" , "brood" , "Plague" , "Be constantly talking about" .)