Seb, taken aback by over-the-top editor, becoming obsessed (8)
I believe the answer is:
besotted
'obsessed' is the definition.
(thesaurus)
'seb taken aback by over-the-top editor' is the wordplay.
'taken aback' says the letters should be written in reverse.
'by' is a charade indicator (letters next to each other).
'over-the-top' becomes 'ott' (abbreviation).
'editor' becomes 'ed'.
'seb' back-to-front is 'bes'.
'bes'+'ott'+'ed'='BESOTTED'
'becoming' is the link.
(Other definitions for besotted that I've seen before include "Head over heels in love" , "Smitten" , "Infatuated - so betted accordingly" , "Stupefied by infatuation" , "much taken" .)