Most ponies would say that if you have the genitalia of a colt, you are a colt. That what you were at birth, defines what you will be for your entire life.
I am living evidence that the opposite is true. That a pony's mind, and a pony's body at birth, don't necessarily match up.
It all started when I was just a small foal. I never felt comfortable wearing suits and ties on the rare formal occasion. I always started to feel sad whenever ponies referred to me as "Shining's brother". My uncle said "maybe he's just jealous". Shining had more friends, he was more athletically fit, and was almost as smart as I was. I guess I might have been a little envious, but it wasn't that which bothered me so much. It was the "brother" part. I was Shining's "brother". A colt. Male. The doctors said it was so when I was born, therefore, it must be so.
Of course, that's a fallacy and blatantly untrue.
I wasn't a colt, and I didn't want to be a colt.
My parents, not knowing what was going on with me, had me start seeing a psychologist every week. They thought that I had depression.
Ultimately, they made no progress. What use is a psychologist when the kid won't even open up? And even if I had, they wouldn't have told my parents unless I strongly implied I would harm myself or others.
So it was for several months. Until one fateful day, I visited the library and found a certain book. On Gender Identity by Big Brains. Out of curiosity, I read through it and suddenly, everything made sense.
I was female in my mind, if not my body. So, I checked out the book and brought it to my parents, excitedly shouting "Look at this, look at this, this is what I am!" because I was so glad to finally know I wasn't strange or weird. My brother, while not as giddy as I was, was perfectly fine with calling me his "little sis".
My parents weren't quite as enthusiastic. They supported me all the way, of course, but they were worried about people who might not support me, the ignorant ponies out there who wouldn't be so understanding. Ultimately, though, after a few weeks, it had seemed like their concerns were unfounded.
So, after a few months, I was officially a filly, even changing my name to "Twilight Sparkle" (My previous name being Dusk Shine), and, bar a few kids on the playground who would pester me as to why I suddenly went by "Twilight" or why I insisted I was a filly, things were going well.
And then I got into Celestia's School for Gifted Unicorns. You all know this story, it's when I hatched Spike. But what you might not know of is the myriad of headlines from Canterlot newspapers, who, once they knew I was transgender, had started printing out headlines like "Princess takes tranny under her wing!" or "The Student's Scandalous Secret: Twilight Sparkle Actually a Colt!"
You can imagine my family wasn't too happy about this. But what really caught me off guard was how readily the Princess had come to my defense. She often, when dealing in politics, tried to stay neutral, but she wouldn't let the tabloids try and smear my name. She would say things like "Whether or not my faithful student Twilight has always been female, is her own private business, and nobody has any right to pry into her private life."
I was touched. I couldn't believe the Princess would care for me that much. It would have been oh so easy for her to throw me away and leave me to deal with all of this baggage, but she had readily come to my aid when I needed support the most. She never told me to keep my issues out of the public eye or to "just admit that you're a colt" like the tabloids did.
I think that's where my idolizing of the Princess came from.
I'm not gay. Not that there's anything wrong with that. But I ain't a lesbian.
"Rainbow, we get it. the more you deny it, the less we believe you. Please shut up." Thunderlane said.
"FUUUUUUUUUUUUUCK YOU GUYS CALLIN' ME A DYKE I'LL HAVE YOU KNOW SOME OF MY BEST FRIENDS ARE LESBIANS AND I.... What are we talking about again?" Whatever. I just know they were being dicks. Shoulda never come to this party...
"Guys, I think she's plastered."
Blossomforth joined in on the conversation, having heard my outburst. "We don't even have any alcohol. That's impossible."
Being drunk-but-not-drunk, I just had to say something stupid and aggressive again. "WHY YOU HITTIN' ON ME FORTHBLOSSOM I TOLD YOOOOOOU I AIN'T SWING WAY THAT! THAT WAY!"
"...Maybe she's drunk off the atmosphere...?"
Several hours of reaffirming my heterosexuality later, Thunderlane's tied up and we're doing the dirty right in his bedroom. Wait, no, it was Blossomforth's. She was the one hosting the party... She's gonna be holding a grudge for a long time.
So, back to Thunderlane and his being tied up, I had not-drunkenly mistaken him for being huge into BDSM, and promptly tied him up and sexed him to near death.... Look, it's not the weirdest thing I did in that state, okay?
"Oh, Thunderlane...."
"HRMHRMHRF!"
"OH THUNDERLANE!"
"HRMMMMF!"
"OH THUUUUUNDERLANE!"
"HRMHRMHRM!"
...It was awkward, and dubiously consensual, though he would later tell me that his only concern during all this was for me. D'awwww. Seriously though, he still has bruises from that night.
One night later, I'm no longer not-drunk and Blossomforth has kicked us both out for not being very nice guests. Because nice guests don't fuck in your bedroom.
While we're walking over to my house for coffee, Thunderlane strikes up a conversation. "So, uh, Rainbow..."
"Don't tell anyone about last night or I will kill you."
"I wouldn't dream of it! But, uh...
"Don't ask if I'm gay either."
"Er, actually, I was gonna ask if you... Wanted to go out sometime?"
I couldn't believe what I was hearing. "After all that last night? Thunder, I..."
"It's okay if you don't want to! If it's too awkward after..."
..."Nah. I'm Rainbow Dash! A little awkwardness can't get me down!"
"Oh, uh, thanks! H-how about Saturday? We can go for a movie or something."
"Sure."
And that's the story of how me and Thunderlane started dating.