You catch them kissing here, and here, and here on the marauder's map. You know that afterward Fred will tell you all about it, but sometimes you've just got to see things for yourself.
There is no such thing as twins.
You are more doppelgangers, modeled after the same boy who has never existed. You are double the incarnation of the same soul. When mum jokes that you are sharing a brain, she has no idea what she's talking about. And that little quirk you have, of finishing eachother's sentences? It goes further: whenever Fred isn't with you, you find yourself saying things he would say anyway, regardless. You anticipate where his words would have gone, and you fill in your part accordingly.
Whenever he doesn't come home, you can't sleep until he is back and you are forehead to forehead. No, no matter how hard you try, you can't remember a time when things weren't like this. Neither of you dates much at Hogwarts because of it - you don't understand the concept of secrets or privacy, and the word 'my' has little to no meaning to you. It feels like spitting out a seed, something that should have been - but coated in sugar or salt, nobody tastes the difference. The truth is, girls don't like your relationship. At first it's cute and everything, and people like twins, but things get complicated quickly. You and Fred are not normal.
First, nobody can tell you apart - not one person on the planet. You are fairly certain that you've switched places hundreds of thousands of times, to experiment, and nobody's noticed. That's how slight the difference is: the only noticable one being that Fred's heartbeat differs from yours by half a second. Nobody would know this, of course, for as much as mum loves you she isn't God; and as far as you know, you are the only one who sleeps pressed into his chest so that you can hear it.
Here's the kicker, though:
Sometimes, even you forget who is who. When that happens, you wait to be greeted in the morning at the foot of the stairs - cos you're always late, and everyone's already at breakfast by then. There's always a small moment of silence, as your famly tries to sort you out - they never can - and whoever ends up being called George first takes on the name. Poor Fred has to sit back and be satisfied.
(Both of you like the initials G.W. better.)
When you're recounting past deeds, you sometimes speak of yourselves in third person. Fred did this and that. George George George. Then one of you might pipe up, remembering which twin you were, and things are set straight again.
With Angelina, things are always straight. Fred knows who he is at all times.
But God, do you know her.
He comes home, telling you of all his exploits, and before you know it you could practically write Angelina's biography, if you ever wanted to. You meaning both of you, of course. It's funny that Fred has something you don't, now - but neither of you ever thinks of it that way, apparently. Angelina becomes a fun little project. You challenge him to do things, and he does them - afterward, you both decide what the next step should be. For her birthday, you both go out searching for presents, and decide on one together. Still, Fred is the only one that gets to touch her - but later, when he's touching you, it's as if all three of you are together.
But it's not like you fancy Angelina, or anything like that. Not right now, anyway. You and Fred have a funny way of going after the same girls, and sure, at first you were maybe jealous. Maybe you tried a little extra hard at practise, and made sure to draw a line between yourself and him. But that's not how it is now it's months, and you aren't even sure if she's pretty or not. You know all about her childhood, all her favorite foods, her birthdate, the history of her family... but when it comes down to it, the thing you know best about her are her affections. She likes Fred a lot, and if given half a chance would like you too, probably just as much.
Suddenly it dawns on you that this is why you're never invited out with them. Shortly after this discovery, you notice that Fred has started calling her 'my' Angelina.
It's a lie, that twins can feel eachother's pain. You didn't feel it at all the time Fred broke his leg, and all those times he burned himself in class you didn't even flinch -- not even with all those half-failed/deadly experiments that left you both black and blue. Half the time, you never noticed Fred's feelings; they became your subconscious. And anyway, it's no surprise: that's usually how it is, with any superstition about twins. It never applies because that's not what you are.
You do feel it, though, the first time he sleeps with her.
You're in the middle of dinner with Ginny, at the very end of the big family table. She's doing some sort of puzzle as she eats, one of those stupid ones from the roadside stands. You've taken it on yourself to give her amusing but terribly false advice, and mum is watching you over her bifocals. All of a sudden, just as you're putting food in your mouth, you get the unmistakable feeling of a hand brushing the back of your neck - it lingers, cold, and disappears somewhere down your shirt. Moments pass with you frozen, eyelid twitching. You touch your hand to your mouth and come away with blood. Ginny is staring, and then she says,
"You okay, Fred?"
It is very hard to look at him, after a while. If you think too hard you start forgetting that he isn't a mirror or a portrait; his features start fading into watercolor. It's the same whenever you stare at your reflection, knowing that no matter what faces you make, no matter what lines you rehearse in the mirror, you will always be him and he will always be you. When you try to fall asleep that night, Fred is unusually quiet; you hold your breath waiting for him to tell you all about it, and eventually you're forced to ask.
"How was... you know?"
And he only shrugs. Both of you look at eachother and close your eyes in what must be perfect unison. You know he is going to speak before he even opens his mouth, and then you disappear into the warmth of his breath.
Regardless, the night you lose your ear everything changes.
This is the first time in your life that you do not resemble Fred. Everyone knows who you are now, and in truth they don't know anything - and not only because you are both the mysterious sort of jester, but because you have no idea who you are, either. At first you cry because it hurts, hurts like hell, and then you find you're crying for an entirely different reason. Fred holds your head in his lap, mumbling, and later you sleep in his arms without ever telling him everything.
When you wake, he is watching you sleepily. "How was...?"
And he doesn't even have to finish before you are showing him.
"George! How did you get those nasty bruises?" asks mum.
Can't be reattached.
These are the words that convince you that you will never be anything.
After what's happened, you are less of a person than before. You're not even a doppelganger now. You are no one's reflection. Fred tries to cheer you, slipping candies in your pocket, and plays tricks on everyone in the attempt to have you smile.
He looks at you, holding your face in his hands:
"That one time in school, when the snackboxes were made--"
"I was you then, Fred."
And one morning, after months of hearing nothing, Angelina appears again in the form of a letter. You take one look at it, and slip it in your pocket.
This is where it gets funny.
When Fred dies, you don't know it until after the dust has cleared - so much for old wive's tales. But even then, you are hollow.
He is smiling, glassy-eyed, wand in hand. One of his legs is bent at a funny angle, and a bright trickle of blood appears between his teeth. He looks nothing like you.