The story examines the nature of love. The student pines for the girl he loves, but his love has no depth or enduring passion. His feelings change abruptly to anger and disgust the moment he is rebuffed. He did not love another; he loved only himself and how he felt as he imagined holding her in his arms while they danced.
Nightingale, however, loved in a way that was completely unselfish. She exhausted herself seeking the red rose he needed to court his love. When it became obvious to her there was no other way to secure the rose, she willingly suffered great pain and sacrificed her very life for the student's happiness. Her love was deep and true.
The theme then takes an ironic turn. The student does not appreciate or even acknowledge what Nightingale has done for him. Furthermore, he judges her "final performance" in cold, derisive academic terms. There is nothing in him that deserved Nightingale's sacrifice.
Nightingale's view of the student was very romantic. She saw in him a reflection of her own heart that was not in him. It did not occur to her that he was not the "true lover" that she was. His unworthiness does not diminish her act of unselfish faithfulness, but it is clear that Nightingale's life would have been much better spent making music for someone who appreciated the beauty of her song.