Director in love, thanks to diatribe beforehand (9)
I believe the answer is:
tarantino
'director' is the definition.
(I've seen this before)
'in love thanks to diatribe beforehand' is the wordplay.
'love' becomes 'o' (In tennis, 'love' means 'zero').
'thanks' becomes 'ta' (UK informal version of 'thank you').
'to diatribe' becomes 'rant' (I've seen this in other clues).
'beforehand' is a charade indicator (letters next to each other).
'ta'+'rant'='tarant'
'in'+'o'='ino'
'ino' put after 'tarant' is 'TARANTINO'.
(Other definitions for tarantino that I've seen before include "Quentin -, US director" , "He makes films" , "Who in tarnation is this US film-maker?" , "Quentin -, American film director" , "Quentin ... film maker" .)