hanahaki is a disease that made the person expel flowers from their body -by coughing or in more extreme cases through other orifices- which It is caused by unrequited love. It will eventually kill the victim if their romantic interest does not return their feelings. it can also be removed surgically, but when the infection is removed, so is the victim's feelings for their love. Ben doesn't want to lose his feelings for you, so he chooses to suffer in silence.