Thanks so much for suggesting this,doublesuicide_yay. However, I made a slight tweak which was that Dazai was with the disease and Chuuya was with someone else. Also, this will be written in Dazai's POV.

I should have never let him go.

I love him. I always have and always will. Who was I kidding when I told myself that I only ever liked Chuuya as a brother? As a companion. As a friend. Even though I repeated that lie every single day... I never thought to correct myself. And now, he's moved on unlike me. He's found himself a sweet maiden that lights up his world like he lights up mine. But I can never tell him that. He's happy now.

But he's happy without me.

He doesn't need me like I need him.

He doesn't love me like I love him.

And it hurts. It hurts like hell. Every day I wake up with that stinging pain in my chest, that aching, dull feeling when I go through my day. But I smile. I smile to cover up whatever scars that it leaves. He's happy. And I should be happy for him. I shouldn't bother him with my pain. I'll only be a burden. I'll only be a nuisance.

I'll hide my suffering for him. I'll tuck it all away like I usually do with that bright smile and casual jokes. Laughing along with everyone else without a care in the world. An airy laugh and an easy grin. I'll continue my somewhat ridiculous suicidal antics, I'll live every day like normal to the rest of the world.

And with a raging storm of emotions hidden within.

I cry myself to sleep every night. The pain inside my chest jabs at me. I cry myself a river. Everything that has been bottled up is finally released into a torrential rain of tears. Grief hits me like a truck whenever I see my Chuuya with his lover. So I let it all out each night. I vent out my anger and suffering until I cry myself dry. When there are no more tears left and only that dull, aching emptiness of unrequited love.

And then comes the first petals.

They're beautiful in their own right. Velvet, vermillion-red rose petals fall from my mouth as I choke up blood. I know that I have the Hanahaki disease. And I know that the cause is my love for Chuuya. But I can't stop loving him. And it's killing me slowly. Literally.

Day by day, the flow of petals grow steadier and they come in heaps, leaving me drowning in my own blood. Eventually, yellow Chrysanthemum petals are added to the mix. Eventually, I'm now coughing up flowers. But Chuuya doesn't know. And as long as he is happy, I'll gladly die for him.

I had to pull a flower out today.

It had grown right up to the back of my throat. I kept choking on it, so it was my only option. When I tugged it free... I had never felt such agony as the roots released their hold from the bottom of my lungs. My very own Chrysanthemum covered in blood.

The same thing happened for the next few days.

I now have a bouquet's worth of flowers. I planted them. Beautiful, blooming roses and chrysanthemums adorned my window sill. At least, now if I die, some part of me will remain with Chuuya on earth. Watching him. Hopefully bringing some joy into his life. They are quite pretty flowers after all. I'll gift it to him in my will after I die.

Chuuya's started questioning me about my health. He's getting more worried about whether I eat or sleep enough. I laugh it off and say that it's the side effect of my new suicidal scheme. We go out to get some ice-cream and go for a walk in the park together. He tells me that he broke up with his girlfriend... that it just wasn't working out. I give him my shoulder to cry on.

It's been sometime after the first petals have started to fall.

I'm in my bathroom. Bandages and clothes stained with blood. The scarlet liquid is dripping from my mouth. It's almost time. Time for me to go.

There's a knock on the door.

It's Chuuya.

"Dazai? Dazai, are you there?"

The door creaks open. We stare at each other.

"Hey, how are you doing?" I give him a lopsided grin.

He starts crying, sobbing. "I'm sorry that I never realised... I'm so sorry, Dazai."

He hugs me.

I tell him that it's fine.

And he cries.

I don't think that he realizes that the one I always loved was him.

But it's too late now.

**********************

I didn't know that he loved me.

I swear that I didn't.

After his death... they found a letter. A letter for me. I didn't know he loved me.

And... the worst part was that even if I knew.

I didn't love him that way.

I hope it made you cry. Or I haven't done a good enough job haha. Also, as Unicat121 suggested, I'll be doing a more happy-ish alternate

ending. And if you enjoyed it, please remember to vote!

Edit: Thank you KIS1OM0 for letting me know about the mistake in the story. I hope that I fixed it.