I wrote this for a fic swap with my favorite author on AO3, plinys, and the word I chose was headache. Note that this is my first ever FitzSimmons fics and I really hope I captured their personalities and relationship alright. Anyway, I hope you all enjoy! (Also the title of this fic comes from a lyric in "Portugal" by Walk The Moon)

Jemma Simmons was a headache; Leo Fitz knew that firsthand. Whether she was teasing him over his dislike of dead things or bickering with him about conflicting theories or decisions, she would eventually just make him sigh in defeat. He just couldn't continue and be threatened by the formation of a headache.

Their competitive bickering or her playful teasing were just small things though compared to what it was about her that really gave him a headache: his worry for her. The two of them had stuck together since college, always going where the other was, and he had formed a bond deeper with her than anyone else he had ever met. So, it wasn't surprising that he easily got worried about her, just as she did him.

He thought about how worried he had been about her after she had caught that Chitauri virus. He didn't think his head had ever hurt so much in one day. He tried to do everything to help her find a cure, er, antiserum, even going in there with her and risking getting it himself. When he watched her jump out of the Bus, he screamed and his head pounded. His headache must have messed with his reasonable thinking because he, the nerdy Fitz, had been so ready to jump out of a plane for her. But that was how much he cared for her.

He had the same feeling when the two of them were about to drown. His head was pounding, he was afraid, but he knew he had to give Jemma the air supply. He just couldn't stand the thought of anything happening to her or anyone hurting her.

When he learned she had disappeared into the Monolith, he blamed himself for a bit. If only he hadn't left her in there, if only he hadn't accidentally loosened the lock, if only...if only. One could only say 'if only' so many times before you just had to accept that what was done was done and you could either be upset over it or do something about it.

So, Fitz started to try to find a way to get her back. He would stay up late trying to study everything he could about the Monolith without actually being able to go to it. Considering the device was Kree it was even harder to study because their wasn't even myth or anything to gather anything off of like with Asgardian artifacts.

Each night that he went without sleep gave him a worse headache each morning after. But he would fight through them just to do whatever he could to get her back. Everyone tried to get him to rest, told him they too were trying to figure out how to get her back, but he couldn't stop. Jemma was his best friend; she had saved him from drowning so he had to return the favor.

Fitz sighed as he looked around the lab, now nothing more than a cold shell since she had disappeared. It'd been months since the incident; everyone else had pretty well moved on, accepted all that had happened. But Fitz couldn't. Jemma was too much a part of his life for him to just find closure in her disappearance, not death as some would call it, disappearance.

He looked over at her side of the lab. He refused to touch any of her things after she disappeared so it sat exactly as she had left it. He wandered over to it and stood there for moment, thoughts of their times together in their running through his head.

Beakers filled with various chemicals that probably needed to be emptied, her microscope with a slide of who knows what still in it, various needles and test tubes laying around. He poked her tablet with his finger but of course it was dead.

Fitz sighed. If only Jemma hadn't talked him into going out into the field then maybe she would be there. But they had had so many good times out in the field, met so many great people, studied things they never would have had the chance to in some Academy lab.

"Jemma, I'm sorry but I feel much more comfortable in a lab."

"We will be in a lab, Fitz. Just one on a plane, out in the field. Come on, Fitz, it will be exciting! We'll get to see so much more than we ever could inside this lab. And I want us to do it together."

Fitz saw the spark in her eye and couldn't help but smile. He did love to see her excitement.

"Alright, Jemma. I'm in."

He traced his fingers over the cold metal of the table. Just when he was got the chance to get closer to her and she was taken away. "You sure have a weird way of backing out of a date," he said with a flat chuckle to the empty room.

"Oh, Fitz, I thought we were still on," said a sweet, English voice from behind him.

He froze for a moment, fearing that he was starting to hallucinate of her like he had before. He slowly turned around and saw her standing there, a shock blanket around her shoulders, Skye standing on one side and Coulson on the other. She gave him a small smile and Fitz was just overcome with emotion.

Jemma was there; she was alive. She was real.

He tried to think of what to say but no words would come that could properly express how he was feeling. He ran over to her and grabbed her in a tight hug. "Jemma," he whispered.

She just stood there for a second, surprised, but then gently wrapped her arms around him. "I've missed you, Fitz."

Fitz could feel feel the headache coming on, the one that always came when you cried, but it was worth it because his tears were tears of joy. The joy that only came when one got their better half back.

"I've missed you too."

Reviews and constructive criticism are much appreciated! ;D