In addition to love (3)
I believe the answer is:
too
'in addition' is the definition.
(I've seen this in another clue)
'to love' is the wordplay.
'love' becomes 'o' (love means zero in tennis).
'to'+'o'='TOO'
(Other definitions for too that I've seen before include "Additionally" , "Moreover, in addition" , "Likewise" , "What a pity!" , "Excessively" .)