Since you talk about a recital, I'd pick pieces from several music periods; only romantic music could be boring. This is an idea for a love recital within a traditional form:
Bach: Prelude 24 (WTK II) or Fugue 23 (WTK II)
Scarlatti: Sonata K99 or K466
Schubert: Impromptu Op 90-3
Field: Nocturne in G Major
Chopin: Mazurka Op 17-4
Schumann: Kreisleriana 2 & 3 or Intermezzo (Faschingsschwank aus Wien)
Brahms: Intermezzo Op118-2 or Op 119-1
Rachmaninoff: Elegie or Prelude Op 23-4 or Prelude Op 23-6
You could substract some pieces above in favour of the adagio of the 2nd Chopin's concerto, which is a declaration of love. On the other hand, Schumann and Brahms composed many unforgettable love pages while having Clara Wieck in mind and heart (And Schumann was succesfull

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