A girl-meets-boy book (6)
I believe the answer is:
missal
'book' is the definition.
(missal is a kind of book)
'a girl-meets-boy' is the wordplay.
'a girl' becomes 'miss' ('miss' can be a synonym of 'girl'**).
'meets' says to put letters next to each other.
'boy' becomes 'al'.
'miss'+'al'='MISSAL'
(Other definitions for missal that I've seen before include "A book containing prayers of the Mass" , "Catholic mass text book" , "book needed to get through service" , "Book of church texts" , "book for complete service" .)