In short Kenma had the hanahaki disease. He was horrified when he found out. He began to feel stuffy and it got hard to breath. He figured it out some time after. It happened right after practice after arriving home from walking with Kuroo. It felt like something was stuck in throat and as he tried to clear it a drip of blood coughed out along with a petal.
It wasn't hard to connect the dots. He knew he loved Kuroo. And he didn't know what to do with himself. Nearly three week did he keep this to himself and it only got worse.
Until it suddenly stopped. His lungs opened up and his coughing fits slowly came to an end. At first he didn't understand. Was it possible he fell out of love? Or did he somehow get lucky? It was as if he were oblivious to the lovesick expression Kuroo had as he stared at him during practice.