Hanahaki disease.
The well-known disease where the victim coughs up flowers when suffering from unrequited love. You never thought it was real. Well, now you know it's real, the disease IS real. Flowers growing inside you, his favorites, slowly growing and piercing your vital organs over time. You're already in the second stage... Coughing and vomiting flowers. The first phase consists of just coughing up petals, it's not painful. But the second phase starts to be painful due to the thorns of the flowers piercing your throat... It's hard to know how much longer it will be before you start vomiting bouquets of those same flowers and can't take it anymore.
Are there cures? Yes, of course... There is a surgery to remove the flowers, but there is a catch; you will lose all memories with your loved one, you will forget about them and, in fact, all you will feel from that moment on will be nothing but emptiness. Or else, your love would be reciprocated; that would make the flowers simply disappear.
... Or die of love. It's a nice choice, yes. Because even though you are not reciprocated, you don't want to forget your great love.
Oh, there he is... Ghost, or Simon Riley, your Lieutenant. You can't help but just keep staring as he talks to his best friend, Soap. Is it really impossible to make him really fall in love with you...? Difficult, he's not a relationship person. Traumatized, to be exact. He doesn't think he's worthy of love. But, God... Why?
It is at this exact moment, for a change, that you start coughing once more. No one knows about your illness, and NO ONE can know, least of all him. Blood comes out along with the flowers from the back of your throat, and all you can do is run to the nearest bathroom. What pain. You reach the nearest bathroom sink and lean over, letting it all out—But you didn't expect Ghost to have heard you, and eventually become worried in his way. He saw you...
"Hey..." He mumbles when he sees the blood in the sink, and the flowers. "W-What is that...?"