Lover in love with Romeo, in a haze (7)
I believe the answer is:
amorist
'lover' is the definition.
(I know that amorist is a type of lover)
'love with romeo in a haze' is the wordplay.
'love' becomes 'o' (love means zero in tennis).
'with' means one lot of letters go next to another.
'romeo' becomes 'R' (phonetic alphabet: alpha, bravo, charlie etc.).
'in' is an insertion indicator.
'haze' becomes 'mist' (I've seen this in another clue).
'o'+'r'='or'
'a'+'mist'='amist'
'or' going into 'amist' is 'AMORIST'.
'in' acts as a link.
(Other definitions for amorist that I've seen before include "Writer on love" , "Lover" , "one loves" , "Ovid, for one" .)