Study heart in love with love once more (2,4)
I believe the answer is:
de novo
'once more' is the definition.
(I've seen this in another clue)
'study heart in love with love' is the wordplay.
'study' becomes 'den' (term for a study or office).
'heart in' indicates the central letters.
'with' means one lot of letters go next to another.
'love' becomes 'o' (love means zero in tennis).
The middle of 'love' is 'ov'.
'den'+'ov'+'o'='DE NOVO'
(Other definitions for de novo that I've seen before include "afresh" , "From scratch" , "Once more, again - in Latin phrase" , "Anew (Latin)" .)