Okay, I'm sorry this chapter took so long! I've been studying for my exams like crazy, and they start next week so I apologise if I don't update again for another few weeks.

Anyway, this chapter is for LisaMichell25 who asked for FitzSimmons Mary's Song. I now have a few different ideas for FitzSimmons songs so thank you all for that!

Disclaimer: I am not Joss Whedon or Taylor Swift so... I own nothing.

Mary's Song – FitzSimmons (AU)

She said, I was seven and you were nine
I looked at you like the stars that shined
In the sky, the pretty lights
And our daddies used to joke about the two of us
Growing up and falling in love and our mamas smiled
And rolled their eyes and said oh my my my

Jemma and Leo had been friends for as long as they could remember. Their parents were friends in high school, and they grew up living next door to each other. Jemma's first detailed memory of Leo and one of their adventures was when she was seven and he was nine.

They'd been playing outside, looking at butterflies and worms and any species of bug they could find. Leo came running over to her with a praying mantis cupped in his hands, yelling at her, "Jemma! Jemma come look!"

Jemma stood up from where she was attempting to dissect a worm and looked at the green bug in Leo's hands.

"Here, you wanna hold him?" Leo asked Jemma.

She nodded her head excitedly and he carefully placed the bug in her hands.

"Isn't he beautiful?" Leo asked. "I bet if we looked real close we could see his spiracles."

"Really?" Jemma gasped, lifting the mantis closer to her face.

"I think so," Leo said, also crowding closer in an attempt to see the bug's respiratory system. "Oh, look, there's one!" He exclaimed suddenly when he saw a tiny hole.

Jemma moved her hands so she could see where Leo was pointing and gasped in awe when she, too, saw the spiracle. She looked up to Leo in that moment, her brown eyes glittering and something about the way she was looking at him… it was almost like, in her eyes, he was more amazing than the stars that shined in the sky.

Mr Simmons and Mr Fitz were sitting on the veranda of the Simmons' house, watching the two children.

"I bet they'll end up getting married, one day," Mr Fitz stated.

Mr Simmons chuckled, but nodded in agreement when Jemma took Leo's hand and led him down to the creek.

"I'll be putting the hard words on that boy in another ten years," Mr Simmons announced.

Both of their wives, standing in the doorway, rolled their eyes at their respective husbands and children.

"Oh my, my, my," Mrs Fitz sighed.

A few weeks later, Jemma and Leo were playing in Leo's tree house in the backyard of the Fitz property.

Jemma was playing with one of the models Leo had made recently, this one a submarine, when she accidently dropped it.

Jemma's face paled as she looked in horror at the broken toy at her feet, well aware of how many hours her best friend had spent putting it all together.

"I'll punch you, Jemma!" Leo shouted, looming over her for a minute before he knelt to the ground at her feet, collecting all of the pieces of his model and clutching them to his chest.

He never did beat her up that day, or any of the times during their childhood where he threatened to punch her. He could never and would never hurt his Jemma.

On Leo's tenth birthday, he had his whole family (and the Simmons') over for lunch. When his mother brought out the monkey cake with ten candles on it, everyone sang Happy Birthday, but Jemma's voice was by far the loudest.

As Leo blew out the candles, he closed his eyes and wished to have Jemma stay as his best friend forever.

He opened his eyes and his mother handed him a knife to cut the first piece.

"Don't touch the bottom, son," His father warned him, "Or you'll have to kiss the closest girl."

Unfortunately, Jemma was down at the other end of the table than Leo.

He carefully pushed the knife into the cake, trying oh so hard to not touch the bottom, but his hand slipped and everyone heard the knife hit the plate below the cake.

The girl closest to Leo was his nasty nine year old cousin, Rebecca.

"No," Leo shook his head, refusing to kiss the nasty, stuck up girl.

"Kiss me, Leo!" Jemma yelled from where she stood in front of her parents.

"Are you sure?" Leo asked. Jemma nod her head in confirmation. "Can I do that, Daddy?" Leo looked to his father.

"Well, she's not the closest girl, but I don't see why not," His father shrugged. "Go ahead."

Leo moved away from the cake and walked towards Jemma. When he was just in front of her, she squealed and pushed her way past her parents, running away as fast as her small legs would take her.

Jemma didn't really think her escape route through overly well, and soon enough she found herself at the wooden fence separating Leo's yard from her own. She turned around to face the boy, grinning sheepishly.

"I didn't really want you to kiss me, Leo."

"But I'm not kissing Rebecca!" He exclaimed. "Ewwwww!"

Jemma's nose twitched slightly as she thought for a moment before saying, "Okay, you can kiss me.

Leo quickly closed the distance between them and pressed his lips to hers for the briefest moment. Neither of the children were aware of the fact that Mrs Simmons snapped a picture of the moment with her camera.

Over the years, Jemma and Leo had only grown closer, their bond increasing tenfold.

It was Jemma's best girl friend, Skye's sixteenth birthday the night that Leo realised Jemma wasn't a little girl anymore.

She was wearing a deep blue cocktail dress and silver strappy heels and spent hours dancing with Skye and their other close friends, Darcy, Maria, Natasha, Betty, and Pepper. The girls' boyfriends, and Leo, stood on the edge of the dance floor watching their girls laugh and enjoy themselves.

Out of nowhere, one of Grant's friends, Antoine, appeared and began dancing with Jemma, his hands resting on her hips.

Grant, Steve, Clint, Thor, Bruce and Tony all turned to watch how Leo would react to the other man dancing with Jemma. All five of them smirked knowingly when they saw Leo's jaw clench and his hands curl into fists.

"Go get her, Fitzy," Clint egged him on.

"Show her how much you care for her," Steve added.

"And give her a night to really remember, if you know what I mean." Tony grinned.

"Tony," Bruce warned.

"What? Oh sorry for being friends with a bunch of old women. I swear the only ones who know how to have fun are Clint and I, and Grant if he's in the mood." Tony said in exasperation.

Leo ignored his friends and walked straight over to Jemma and Antoine.

"Hey, Jemm," Leo said as he placed his hand on Jemma's shoulder.

The girl turned her head to look at him curiously, "Yes Leo?"

"Can I talk to you for a minute?"

"Of course," She said immediately before looking briefly at Antoine, "If you'll just excuse us for a minute." She turned back to Leo as he walked off the dance floor. Jemma quickly tried to catch up with him.

"Leo, what's wrong?"

He didn't respond.

"Leo, what is the matter?"

Again, he didn't answer.

Jemma was getting annoyed by this stage, and her voice rose slightly in anger, "Leopold Fitz, tell me what is the matter with you right this instant or-"

Leo turned around quickly and pressed his lips to hers, effectively shutting her up. He pulled back and looked down, blushing. "I just didn't like you dancing with him."

"Oh Leo," She whispered, running her fingers over his cheek lightly.

As she touched his face, she noticed how his blue eyes shined like pretty lights.

That night when Leo walked Jemma home, they stopped on the footpath at the place where their fences joined hoping that neither set of parents would be able to see them there.

Leo pressed his lips to Jemma's again and she wrapped her arms around his neck, pulling him closer as she kissed him back.

Little did the pair know that Leo's parents and Jemma's parents were watching their interaction intently from the second story of their respective houses.

"I never believed they'd really fall in love," Mr Simmons muttered quietly, but Mr Fitz could still hear him through the phone.

"You better start practicing that speech to warn him about what you'll do if he hurts her," Mr Fitz replied jokingly, but he too was in mild shock about the development of their children's relationship.

Mrs Fitz stood slightly behind Mr Fitz as they looked out the window and rolled her eyes.

Mrs Simmons was standing beside Mr Simmons looking out the attic window and said, "Oh my, my, my."

Leo and Jemma often went on late night adventures after that. He'd drive them to the edge of their town, or the park, or the creek-bed, or wherever they could see the stars shining down.

They got to the creek-bed at two AM one Saturday morning and climbed out of his truck, making their way to the bank and lying down beside each other, not touching except for their joined hands.

That was the night they had their very first fight. It was stupid really, what they were fighting over, but they both were incredibly stubborn and soon a silly little argument turned into a full-blown shouting match.

Jemma demanded he take her home immediately, and they refused to talk to each other for the whole car ride back to their houses. She got out of the car when he pulled up in her driveway and slammed the car door with far more force than necessary.

Leo scowled at her back as he watched her walk to her front door which she also slammed behind herself. He then reversed his car out of her drive and parked it in the garage of his house.

He got out of the car and locked it, closing the garage before he began walking to the front door. He had reached the door and had his key in the lock before he realised how ridiculously stupid they'd both been.

He pulled his mobile phone out and called Jemma, but it went straight to message bank, so he pocketed his phone and keys and then walked to the small gate in the fence separating his and Jemma's backyard.

Leo sat in a tree near the back of Jemma's house and his eyes settled on her bedroom window, following her silhouette against the closed curtain until she turned off the bedside lamp. He stayed outside until morning light.

When Jemma pulled back her curtains at about 10am the next morning, she saw him asleep against the old tree they used to climb when they were still kids.

"Oh my, my, my, my…" She whispered slowly and smiled softly to herself.

A few years had gone and come around. Jemma was 24 and Leo was 26, and they both were scientists for a secret, non-government agency, the name of which is classified.

Luckily the agency had a base of operations just outside of Jemma and Leo's town, so they hadn't had to move away for work. It was weird, most of their friends also worked for the agency. It was like their town bred secret agents or something. That was Leo's theory, anyway.

They were sitting at their favourite spot in town, just outside the park, when Leo looked at Jemma and got down on one knee.

"Jemms," He began as he looked up at her and took both of her hands in his. "You have been my best friend for as long as I can remember. Everything we have ever been through, the good and the bad… It just shows that we can make it through anything as long as we're together. I can't imagine my life without you, and I was just wondering if maybe you'd like to marry me? Or not, but that'd make things kind of weird if you said no…" He was rambling nervously.

"Oh Leo," Jemma chuckled at him, "Of course I'll marry you, silly."

"Really?!" He asked hopefully.

"Really," Jemma smiled in confirmation and Leo pulled a simple white gold ring with one diamond nestled on top out of his pocket.

"I like to think about the law of thermodynamics," Jemma began speaking her vows.

"No energy in the universe is created, none is destroyed," Leo whispered, smiling.

"No energy in the universe is created, none is destroyed," Jemma confirmed more loudly, smiling at him. "That means that every little bit of energy inside of us, every particle will go on to be a part of something else, maybe live as a dragonfish, a microbe, maybe burn in a supernova. And every part of us now was once a part of some other thing: a moon, a storm cloud, a mammoth…" She smiled softly at Leo and added, "A monkey."

Leo smiled and allowed a few tears to roll down his cheeks.

"Thousands and thousands of beautiful things that were once terrified to die. We gave them new life, a good one, I hope. It's fitting that we're doing this together. I can't wait to spend the rest of my life with you, and maybe when we eventually die the particles inside us both now will be within something else together."

Leo smiled, the tears sparkling in his eyes. He recited his vows to Jemma and the gathering of people who had attended their wedding: "I couldn't live if you didn't, Jemma. You always said how I was your best friend in the world, but for as long as I can remember you've been more than that to me. I couldn't find the courage to tell you for so long. Even after we began dating, I didn't tell you I loved you for 17 months. So I'm glad you let me show you, you let me show you how much I love you when you said you'd marry me. I hope I can show you every day from now until we're a hundred years old. I promise to love you and I will always keep you safe no matter the consequences. You will always be my best friend and so much more."

The priest smiled at them both broadly, "Do you, Jemma Simmons, take Leopold Fitz to be your husband forever more?"

"I do," Jemma smiled as she looked up at Leo and slipped the simple wedding band onto his finger that Grant passed to her.

"Do you, Leopold Fitz, take Jemma Simmons to be your wife from this day forth?"

"I do!" Leo said enthusiastically, causing everyone to laugh and Skye to nearly drop the ring she was holding for him as she doubled over in laughter.

When Leo had put the ring on Jemma's finger, the priest smiled and said, "I now pronounce you husband and wife. You may kiss the bride."

Leo needed no further encouragement and wrapped his arms around Jemma's waist as he kissed her.

When they walked down the aisle together, both saw their mothers crying and the smiling faces of basically the whole town.

At the reception, Skye stood up to do her Maid of Honour speech.

"Now, I'm sure most of you are expecting me to babble on for hours, and I probably would have except Grant and Natasha already warned me to keep my speech as short as possible. So, I will heed their request and keep it short and sweet, just like Jemma!"

Everyone laughed while Jemma glared up at her best friend.

"So, according to Greek mythology, humans were originally created with four arms, four legs and a head with two faces. Fearing their power, Zeus split them into two separate beings, condemning them to spend their lives looking for their other halves. Now, I think you'll agree with my theory that Jemma and Leo are each other's other halves. Put together, they are unstoppable. They can, have and will achieve anything they put their minds to, so long as they're together. So, if you'll all raise your glasses with me; to Jemma and Leo."

Fifteen months later Jemma gave birth to hers and Leo's first children, a pair of twins which they named Alison Lucy and Christopher James.

Three days after they were born, Jemma and Leo took little Alison and Christoper home to the house where they met so many years before. As they stood on the front porch of Leo's parent's house, they both thought about the stories they had been told of the time they first met when Jemma was barely two and Leo was four.

Suddenly, Leo looks up from Alison's face and met Jemma's eyes, "After all this time, you and I."

Jemma smiled back at him, "I'll be 87, you'll be 89, I'll still look at you like the stars that shine in the sky."

Neither of them heard their two mothers standing just inside the house as the older women both whispered, "Oh my, my, my…"

I hope you liked it!