They are eight years old, chasing each other round the orchard behind The Burrow. Nymphadora slips in the mud and falls, and Charlie trips over and lands on top of her. They roll over in the mud like a pair of puppies, giggling madly.
"You're my best friend, Charlie," Nymphadora says, still laughing.
"Always," he tells her.
(Their mothers are not impressed by the muddiness of their clothes.)
They are eleven years old and waiting to be Sorted.
Nymphadora is worried. "It'll split us up," she moans to Charlie, ignoring Professor McGonagall's stern look.
He grins, although he is worried too. "Doesn't matter," he says bravely. (He is Gryffindor already, although the Hat hasn't said so yet). "We'll still be best friends, Dorie."
Nymphadora is before him. "Hufflepuff!"
She winces. Charlie won't be a 'Puff, that's for sure.
He looks over at her as he goes to join Bill at the Gryffindor table. "Always," he mouths silently, and somehow Nymphadora knows it won't be as bad as she fears.
They are thirteen years old, and almost enjoy Potions because it is the only lesson the Gryffindor and Hufflepuff third years have together.
"Miss Tonks, Mr Weasley, could you put some tiny portion of your minds to your work?" Professor Snape sneers, as they whisper together behind their shared cauldron.
They pay him no attention, and the potion is a disaster. (Not that either of them care very much.)
"I hope you consider your little chat-fest was worth a detention," Snape says coldly to them.
"Always," Charlie tells Dorie with a grin, the minute Snape's back is turned.
They are fourteen years old, and Dorie is crying in the corner of the library because Declan Fitzpatrick has dumped her.
Charlie finds her, and wordlessly offers her a hanky and a bar of Honeydukes Best. She snuffles into his chest, and he holds her tight, even though he hasn't a clue what to say to make her feel better.
"I'm glad I've got you, Charlie," she sniffs.
"Always," he tells her.
They are fifteen years old, and Tonks is going out with Bill.
"It won't stop us being friends, Charlie, will it?" she asks him anxiously the day after Bill asks her out, and she says yes.
"Of course not," he says, hoping the tone of his voice is not too bright to be believable. "We'll always be best friends, Dorie."
(Why did it take this to make him realise how he feels about her? He cannot hate her, but he would happily murder his brother.)
Charlie is sixteen, although Tonks won't be for another six weeks.
Bill and Tonks have scarcely spoken to each other since they split up a month ago. Charlie doesn't want that to happen to him and Tonks. He'd rather have her as his friend than not at all.
On the Hogsmeade weekend in February, things happen by themselves. Somehow they end up walking out of The Three Broomsticks hand in hand and it feels right and natural. A while later, they find themselves in an alley behind Zonko's and it is some time before they want to talk about anything.
When they finally pull apart, Charlie looks down at Tonks with a smile.
"My girl?" he asks, his eyes twinkling.
"Always," she replies.
They are eighteen, and it is summer, and exams are over, and everything should be wonderful, but it isn't.
"Why do have to go so far away?" She knows why, but she thinks it might hurt a tiny bit less if she puts the blame for this on Charlie.
He sighs, and slumps down beside her on the grass. "You know why, Dorie," he says quietly. "There aren't any decent-sized dragon reserves in this country, and I might never get another chance like this." He shrugs resignedly. "I have to do this."
"I know," she says in a small voice. Her hair is drab brown, her face hopelessly sad. "And I have to do what I have to do."
She turns away from him, biting back tears. He sighs and buries his face in his hands.
After a bit, she turns back to him. "We can still be friends, though, can't we?" she asks.
He manages a smile for her. "Always," he says.
They are nineteen, twenty, twenty-one and they see each other once in a blue moon. They don't write beyond postcards, because neither of them is much of a correspondent, but they Floo-chat now and again, and hear about each other via their mothers, or Charlie's dad, whom Tonks sees sometimes at the Ministry.
When they do meet, it's as if they've never been apart. They talk and laugh and drink, and sometimes they sleep together, because, hey, they love each other, and neither of them has anyone else serious, and who is it hurting?
"Are we still best friends, Charlie?" a very drunk Tonks asks him one night in a bar in Cairo. (They are both visiting Bill, but he has to work tonight.)
"Always," Charlie assures her. He is not quite as drunk as she is, and he makes sure they both get back to Bill's flat safely.
They are twenty-two, and suddenly things are different, darker, dangerous. They are both members of the Order of the Phoenix, although Charlie still isn't around much.
And Tonks is beginning to have feelings for someone else, although there are so many reasons he is wrong for her. But it feels right – even if the man concerned refuses to see it himself.
Charlie is the first person she confides in, one night during one of his rare weekends in England, a night when they are both bored silly watching a Death Eater gathering that never materialises into anything more than a gathering. He listens and sympathises and tells her to go for it (and ruthlessly suppresses the feelings of jealousy her revelations unexpectedly inspire). Tonks smiles and kisses him, and tells him yet again that he will be her best friend forever.
"Always," he agrees.
They are twenty-three years old, and Tonks is suddenly engaged to Remus Lupin.
Charlie finds out in a scribbled almost illegible postscript to Bill's letter, written two days after Greyback attacked him. (The rest of the letter is in Fleur's spiky French handwriting, but Bill obviously didn't want to dictate this bit to her.) Charlie wishes that Tonks had told him herself, but the next day, he gets a letter from her, and she is so happy, and she is so clearly in love with Lupin that he can't help but smile for her.
He sends the two of them a congratulations card, hoping they will always be happy. He knows Dorie will understand.
(He does not go to their wedding. Bill and Fleur's wedding less than three weeks later is a good enough excuse for not being able to get leave. He is glad of it.)
They are twenty-four years old and Tonks has a son, and they are fighting, and everything seems hopeless, but they keep going because they have no choice.
Then, abruptly, it is all over, and the world is free again.
Tonks is dead.
Charlie is twenty-four years old, and Tonks will be twenty-four for ever.
He does not know how he gets through her funeral, just two days after Fred's, but somehow he does. Among the bouquets and wreaths on the grave is a single pink tea rose with a simple label bearing one word: "Always."