Here's what he discovers:
Once the victim is vomiting entire flowers, the disease has entered its final stages. If left untreated, the victims lungs will be filled with the flowers and roots growing in their respiratory system. They will choke on their own blood and petals and die.
Aside from the object of the victim's affection realizing/confessing their love, the flowers can be surgically removed. However, this will remove the victim's feelings of love towards their beloved, as well as their ability to love, romantically or platonically, ever again. The victim will also lose all memories of their beloved.