The Prompt: It’s clear to everypony that Rainbow Dash and Fluttershy are a couple. Everypony except Rainbow Dash and Fluttershy.
Dashie-
I'm writing this letter from the train to Canterlot. I'm sorry I never told you, but even if I did it's not like you'd even notice. I know what's going on with the two of you, and it makes me look like a even bigger fool than I already do. I know it seems like I don't care about those things, but I do, Dashie. I'm not a fool. I see how you look at her and how much time you spend together, and how when you come back from "giving her flying lessons" you blush uncontrollably. I know you care about me, but I know you love her more than you'll ever love me and I can't stand being second choice, so I'm letting you go. I know you'd never let yourself cheat or leave me even if you wanted to, so I'm letting you go. You can have her now and be free to love her. History always wins, Dashie. Even when we first began dating, I remember now how you talked about how beautiful my blue eyes were, and how much you loved blue and green eyes.
Well, I might have one, but her eyes are both those colors. I should've seen it sooner. I remember when you started giving her flying lessons. I was sure you were just trying to help, until I went to visit Rarity, and when I walked in she said in a pitying voice "Oh, you poor thing.." and started telling me how pegasi were never faithful. I didn't get what she was saying until she asked, "What's Rainbow Dash doing right now?" and I said, "Giving Fluttershy flying lessons!" and Rarity said, "Pinkie, dear, does Fluttershy really seem to need flying lessons?" and I thought about it, and I said, "Well..no."
And then I realized what she was saying, and I refused to accept it. "She would never cheat on me, silly! Not my Dashie!"
And you didn't. But I know how you always think about her, and how when I asked what your favorite color was, instead of saying "All of them, silly!" and kissing me like normal, you said in a really distracted voice "Yellow. Light yellow."
Who do we know who's yellow, Dashie?
I hope you go tell her how much you care about her now. Then you two can be a couple and everypony will be happy, not just me.
And me? Don't worry about me. I'll find some work somewhere, and I'll keep making ponies smile just like always.
I bet you and Fluttershy will always smile now. Will you, just for me?
Love you, Dashie.
Pinkie.