Is he a Romeo to a girl? (6)
I believe the answer is:
oliver
'is he' is the definition.
'a romeo to a girl?' is the wordplay.
'a romeo' becomes 'r' (phonetic alphabet: alpha, bravo, charlie etc.).
'to' means one lot of letters go next to another (I've seen this in other clues).
'a girl?' becomes 'Olive' (girl's name).
'r' after 'olive' is 'OLIVER'.
(Other definitions for oliver that I've seen before include "Dickens-based musical" , "First name of Goldsmith, great 18th century Irish writer" , "One taking pride in food" , "Orphan recruited by criminal gang" , "A Cromwell, a Twist" .)