Immortality, to many, is seen as a gift. A gift to those who have earned it, to those who deserve it. Celestia, now counting millenia, merely sees her age as nothing but a number. Her lover, however, is not so gifted.
These thoughts eat at the Princess of the Sun, and they keep her awake at night.

After Fluttershy tells Rarity of her engagement, Rarity considers the nature of love and her own happiness.

Luna ponders her life, before and after she was banished to the moon.