Fred and Arya were both running through the castle to find each other.
"Herm, have you seen Ary? I need to find her and tell her that I messed up big times, but I realised how I really feel" Said panicking, frantically searching around Hogwarts.
Hermione was having fun with Krum and didn't know anything about her friend.
"I don't know, I lost sight of her since the beginning of the ball"
Fred run away, muttering under his breath.
"Thanks Hermione, that's really helpful" Said continuing searching, determined to find Arya and make things right.

After a while, Arya run into someone in a deserted corridor. She stopped and looked at the boy in front of her.
Only a few meters separated them.
"Fred"
Fred saw her and couldn't help but feel a pang in his chest. On the other hand, he was surprised and relieved to see Arya, so slowly went over to her.
"You look beautiful, Arya"
She blushed and looked down.
Fred took her hands in his, so she lift her face and looked into his eyes.
"I've been looking for you everywhere. I need to tell you an important thing"
"I'm listening"
He leaned closer and whispered.
"I'm sorry for being a playboy and for hurting you. It took me kissing someone else to realize that I only want to be with you" Said waiting nervously for a feedback.
"But you said you weren't looking for a relationship and you didn't want one because you couldn't give me what I need..."
"Yeah, I know what I said, but being away from you and seeing you with someone that wasn't me, made me realize that I don't want to lose you. I don't want to keep my freedom if it means losing you. I want to be with you, darling, and I promise to give you everything you deserve. Will you give me another chance?"
"Seeing you and Angelina kissing wasn't the best..."
"You don't have to worry about me liking anyone else, babe. I've had my eye on someone special for a while now, someone I've got to know better through the years" Said giving her a gentle smile.
"Are you sure?" Said Arya squeezing his hand.
"Darling, I don't love her, or anyone else, not the way I love you. She was just an infatuation compared to what I feel for you. I'm sorry for making you wait, but I promise, my heart is yours" He softly kisses her lips, lost in the moment.
Arya stepped back and whispered on his lips.
"You are the only one I deserve, we can learn together how to be in a relationship, but if I give you another chance, do you promise to not hurt me anymore?"
Fred run his hand in her hair.
"Yes, I promise to not hurt you anymore. I will do my best to make this relationship work and to always put our love first" He took her hands again.
"So, can we end the night in a special place?"
She smiled.
"What do you have in mind?"

Fred and Arya went to the astronomy tower, full of beautiful memories for the two of them.
Fred wrapped her in his arms and kissed her under the stars, sliding gently with her to the rhythm of the music that could be heard in the distance from the great hall.
Arya placed her head on his chest and smiled at the sound of his heartbeat.
"I'm happy to know you realised your feeling, I couldn't believe you fell in love with me"
He smiled and kissed her forehead.
"That's what love does, it makes even the cynics believe in it" He leaned in for another kiss.
"And I'm so glad to make you happy, darling. I promise to never let you down"
She cupped his face.
"I know, Freddie, I trust you"
He kisses her hand and with a spell he made a mistletoe appear above them.
"I promise to spend every day making you laugh and loving you with every bit of my soul from now on. And one day, when we're ready and the time is right, I'll get down on one knee and ask you to be mine forever. Nothing would make me happier"
They kissed softly under the stars.
"Merry Christmas Freddie, your love is the best gift ever"

***

Month passed by. Fred and Arya, after confessing their feelings to each other, decided to try again from scratch. They went out on different dates every day, and at the end of her fourth year at Hogwarts, Fred officially asked her to be his girlfriend, now sure that his feelings were true and there was no place for anyone else in his heart.

Time passed and Fred kept his promise, showing Arya how much he cared and that he wanted only her as his girlfriend.
One day, he surprised her with a bouquet of her favorite flowers, telling how beautiful she was and how lucky he felt to have her in his life.
Fred also made sure to steal kisses whenever they're alone, making Arya blush but also feeling loved and cherished.
He took her out on fun and adventurous dates, always making her laugh and forget all worries.
Arya could see how much Fred was changed for the better, always putting her first and showing her that he was the loving, protective guy she deserved, and with every passing day, their bond grew stronger.
Fred and Arya, taking on the world together.

Even in the dark times during Voldemort's rise, their love was stronger than ever.
Fred and Arya just turned twenty and eighteen years old, everyone at the Burrow was afraid for the imminent war.
Fred stepped forward, a protective stance in front of Arya.
"She is my soulmate and I cannot leave her behind. I promise to fight with strength and determination, for her and for our future together. She is the love of my life and I could never bear to see her hurt, I promise to be strong and brave, and come back to her, no matter what"

And when the war started, Fred was ready for the big step. Maybe was the tension of the war and the fear of losing her, but during a cold night, he asked her to marry him.
"Age does not determine maturity or love. What matters is how we feel for and treat each other. I know what I want and who I want it with, and that's you, darling. And as long as you choose to be with me, I will always love and protect you"
Fred took out two wedding rings from pocket.
"I'll love and protect you always, my wife"
He slipped it on her finger.
"You're my greatest adventure and I can't wait to share countless more with you by my side as my partner in life" Said as a tear rolled down his cheek.
She slipped it on his finger.
"I promise to stay by your side, cheer you up and love you until the end of our days" Said wiping away his tear.
After composing himself, Fred pulled her into a tight hug, never wanting to let go.
"I love you more than I can put into words, let's face whatever comes our way together"
He kissed her passionately.
"Nothing can ever tear us apart"

But timing wasn't right.
Fred tried with everything in his power to come back to Arya alive, but Voldemort's followers were stronger.
This was the only promise he failed to keep. But Arya would never leave him alone. Being the brightest and strongest witch of her age, she participated in the war to avenge the boy who loved her very much, sacrificing her life for the magical world.
In the end, the two still managed to find peace and infinite love, even if in another world.

The end.

A.N. Don't hate me, I just followed what J.K.R. wrote. In alternative, Fred doesn't die, they end the war and decided to marry in front of their families and friends too, they had their own house, Arya was an alchemist as she dreamed and Fred was working at the prank's shop with his brother. They lived forever happily ever after. You can choose if they had kids or not.