Narrator
A young, love-struck man whose journey from adolescence to full-fledged adulthood takes the form of a symbolic dream he has at the age of 20 in which he becomes religiously addicted to a flower.
"The Rose"
In the context of the dream, the rose is just a literal flower, but because the narrator says that the events of the dream really do come true, we can take the rose to represent a young maiden with whom the narrator falls in love. By "hiding the rose" from him, their community can be seen to be keeping them apart, like Romeo and Juliet (although this story is way older than Romeo and Juliet). Even as an image in the dream, the rose is a poetic representation for a girl.
Cupid
This meddling, mischievous god is the representation of romantic love in the Roman myth. By involving him in the poem, the poet draws our attention to the helpless, religious fervor of the boy's love for his beloved. He feels compelled by the gods. He feels they are fated to be together, but that's just the effect that Cupid has on people. He makes them into fools for one another.
Narcissus
By invoking the character of Narcissus, the narrator explains that the center of the plot revolves his ability to love himself. Narcissus is the god who looks into the fountain and falls in love with his own reflection.
Garden Guardians
Another pair of mystic characters are the guardians who seize the beloved from the dreamer. They represent the forbidden quality of the unknown.
Lady Reason
Lady Reason is a common medieval personification of wisdom. She is commonly invoked as an anti-romantic image, standing between the lover and the beloved to try and talk some sense into the kid. She's the force in the back of his mind saying, "Please slow down and use your head."
Nature
Nature itself becomes a personified character later in the poem during Jean de Meun's meditative, philosophical ending.