A poison ( cynari )

Tighnari had the biggest crush on Cyno but he knew his feelings belonged to Nilou. He try to ignore his feelings but one day coughed Up flower petals. When he went to to the nurse she told him he had Hanahaki Disease in which the victim coughs up flower petals when they suffer from one-sided love. It ends when the beloved returns their feelings or when the victim dies. It can be cured through surgical removal, but when the infection is removed, the victim's romantic feelings for their love also disappear.