'My fragile leaves,' it said, 'his heart enclose.' (6)
The fragility of the rose's leaves implies that there's something weak about using this natural element to express one's feelings. It could be the gesture, or the man sending the flower, or maybe both.
Love long has taken for his amuletOne perfect rose. (7-8)
Hmm, a rose is a good amulet, or source of protection, because it has a thorn. That also means it's not a great symbol of love, because it has the potential to hurt people you love. Eek!