Believing isn't easy.

Mulder didn't wake up one day suddenly believing in all things supernatural. His propensity to believe developed gradually over many years, set in motion by his sister's unexplained disappearance. When he studied at Oxford, he made a hobby of researching alien abductions. He kept his hobby a secret from his professors and peers, lest he become the subject of ridicule and ostracization. At the FBI Academy, he continued secretly searching through archives, seeking evidence and first-hand accounts of the paranormal. The more he found, the more his curiosity grew.

Discovering the X-Files opened up an entirely new dimension to his research. By the time he found the X-Files, he was already primed to believe. The plethora of new information at his disposal triggered a tipping point, pushing him over the edge. What was once a hobby quickly transformed into his life's work.

Mulder never gained anything from believing. His life wasn't made any easier or more comfortable by chasing lights in the sky or tracking down the latest thing that goes bump in the night. Despite all he found and all he experienced, none of it brought his sister back, which was the true reason he began this journey in the first place.

When he and Scully were in Antarctica, Mulder witnessed what he considered indisputable evidence: proof of an extraterrestrial virus, propagated by honey bees, gestated within human hosts to produce a new life. An alien life.

They saw a freaking spaceship for fuck's sake.

In his hands, he held a vaccine for the virus – proof even Scully could believe. Of course, he used the vaccine to save her life and no longer had it in his possession. Isn't that the way it always happened? How many times had he been so close to the truth, only to have the tangible evidence slip through his fingers?

Antarctica felt surreal yet simultaneously more real than anything he had ever experienced. Drunk on a potent cocktail of adrenaline, panic, and the animal instinct to survive, Mulder had been hyper-aware of every detail of his surroundings. He tried to notice everything and store it in the banks of his memory. After pulling Scully to safety, the spaceship broke through the ice like a whale breaching the ocean's surface. That's one image he will never forget. On his deathbed, he will still remember the way the sun's light flared off the metallic surface of that ship.

If only Scully had been fully conscious, she would have seen it too. Unfortunately, instead of witnessing the most breathtaking phenomena of their lives, Scully was barely able to keep her eyes open. Rescued mere moments before from becoming a human host of a malevolent extraterrestrial biological entity and on the verge of a nasty case of hypothermia, Scully didn't see it.

Despite the circumstances, Mulder was profoundly hurt when Scully denied the nature of the virus, claiming that all she could prove with science was that it attacked human cells.

Tell that to the long-clawed alien he saw burst to life in the cryogenic chamber next to hers.

When he showed her further proof, the photo of the man whose stomach cavity was ripped to shreds by one of those creatures, Scully doubled down. She dug her heels in, determined not to believe. Over the years, he came to crave Scully's validation the more she withheld it. When they investigated particularly unbelievable cases, that's when he wanted her credence the most.

Each rebuttal stung like betrayal. Even if she didn't see it, even if the alien was not burned into her memory the way it was with his, why couldn't she simply believe him?

It wasn't the first time they butted heads, of course. They approached each case from very different viewpoints and schemas. Their partnership was stronger for it. It was the reason their success rate was better than any of their predecessors assigned to the X-Files. Their strength was in diversity of thought. While their arguments may be lively and sometimes heated, they were always respectful.

The way they fell into their well-worn roles was like a dance. They knew the steps by heart through muscle memory, challenging and prodding each other in the same ways over and over. The only perpetual unknown was: Who would convince the other first? Who would concede that the other is right? But this was not a case of a swamp monster, a moth man, or el chupacabra; this could have been the fruition of his entire life's work.

Mulder was sick of the dance. The denial of what happened between them right before she was stung by that bee was yet another two-step he and Scully were performing.

They almost kissed. He still couldn't fully wrap his head around it. For all the minutiae he remembered about the spaceship in Antarctica, he remembered almost kissing her even more. It was painful how much he remembered about that moment.

Her eyes fluttered. Her lips parted. She leaned in, tilted her head. Maybe it was only an infinitesimal amount – the leaning in, the tilting – but he would swear on his life that it happened. Right before, when their lips were about to touch, she took the tiniest inhale. It was barely a whisper. An anticipatory breath.

He poked at the memory incessantly, pushing it back and forth the way a child would with a loose tooth. She was going to kiss him back. That's the part that had him reeling.

There were plenty of mental gymnastics to rationalize why she would kiss him. Maybe it was simply a fleeting moment of vulnerability. After all, she had just resigned from the FBI, prepared to walk away from everything. Her career, or at least her career with the FBI, was over. Their five-year partnership was about to end. When she came to his apartment, she was visibly upset, shaken by her meeting with the Office of Professional Review. Her life was about to be upended right when they were closest to discovering the truth.

All the hand waving in the world, however, didn't change the way her eyes narrowed as he leaned in to kiss her. It didn't change the insistent press of her fingertips on the back of his neck, urging him closer. It didn't change the raw tenderness he saw in her eyes when he held her face in his hands. He didn't imagine it.

In the heat of the moment in his dim hallway, he didn't want to deny his feelings anymore. What he felt for her was real and blinding in its intensity. However, usually what overshadowed those feelings was the even more intense fear of losing her. Nothing was worth the cost of losing her. He learned that the hard way when she was abducted and then learned it all over again when she was diagnosed with cancer.

The way they avoided the topic of that earth-shaking moment made her dismissal of what he saw in Antarctica somehow much, much worse. Logically, he knew those two things were discrete events, completely unrelated, but his brain wouldn't allow him to fully compartmentalize them. Every time she said, "I don't know what I saw," he heard, "I was not going to kiss you."

The thought was irrational, nonsensical, and unfair to Scully. Still, he couldn't seem to stop this bespoke form of masochism.

The strain in his relationship with Scully made Diana Fowley's resurgence in his life that much worse. Diana gave him what Scully didn't. Diana didn't question him, challenge him, make him jump through hoops to be believed.

From the moment Diana Fowley joined the Gibson Praise case, Scully's distaste for her was palpable. He wasn't sure he would describe her behavior as overt jealousy, however, it didn't take a mind reader to intuit her immediate distrust. He didn't tell Scully about his prior romantic entanglements with Diana, therefore, he concluded that her reticence to trust must be purely professional. It was understandable. With Diana's background in parapsychology, there was a shorthand between her and Mulder that was simply different from the kind he had with Scully. The two women had diametrically opposing viewpoints on almost everything. The only thing they had in common was their fierce loyalty to Mulder.

Diana believed him about the creature and led him straight to the reactor where it was hiding. As a punishment, he and Scully were removed from the X-Files. The meeting was a formality, he assumed. It was a foregone conclusion that was probably set in motion the minute he got too close to the truth.

Flagrantly disobeying their superiors' orders to stay out of the basement, Mulder continued his work in their former office. Scully found him sitting at his desk, trying to recover more burned X-Files. At that moment, he wasn't sure if he was ready to talk.

With his back to her, he said curtly before she could start, "It would help if you'd shut the door. It'd make it harder for them to see that I'm totally disregarding everything I was told."

She closed the door behind her. "Everything we were told, Mulder."

There was a shade of accusation in her voice. Mulder hadn't been playing nice. Whatever Scully came to tell him, whatever scolding she had in mind, he was in no mood to hear it.

"They can't take away the X-Files, Scully. They tried." He went back to staring at the screen, avoiding her eyes.

"You know Agent Fowley's report to OPR painted the facts in an interesting way. I hope you haven't been betrayed."

And there it was. Right back to Diana. Scully didn't get it. Diana worked the system, operating within its bounds to not arouse suspicion. The men at the top had to believe she was playing by their rules. It was the only way they could continue their work without pissing off those with the most power.

"Agent Fowley's report was a means to an end," he replied, "trying to protect the work. Protect the X-Files."

"Mulder, Agent Fowley's report states that the man you saw attacked was bludgeoned by an unknown subject. She makes no mention of a little boy who as it happens is nowhere to be found."

His annoyance began to surface, becoming harder and harder to hide. He swiveled around to look at her, his jaw tense, ready to argue.

Scully finished, "It would seem that her report protects everything but you."

If only Scully knew. His relationship with Diana ran deep. Saying they discovered the X-Files together was leaving out vast swaths of history and emotion.

From the start, his relationship with Diana was like fire. When they met in the Academy, sparks flew immediately. Their chemistry burned white hot. They didn't waste any time, tumbling into bed together within a week of meeting. Mulder threw caution out the window with her. Before he could catch his breath, they were in a full-fledged relationship. He fell deeply in love with her to the point where it became an obsession. He didn't give a damn about professionalism or FBI rules on fraternization between agents or the inevitable consequences. He was young and naive then. He didn't know yet how people could be made to disappear.

When they discovered the X-Files, Diana already knew everything about him – about his sister and his theories about her abduction. She recognized the importance of the X-Files and how it could potentially answer all the lifelong questions that plagued him. That, along with her academic background, made Diana the perfect fit to partner with him. Diana advocated for the re-opening of the X-Files as much as Mulder did.

After that, Diana was no longer his only obsession.

Professionally Mulder and Diana shared the same vision and passion for the X-Files, but their personal relationship became fraught with issues. All the things Diana had loved about him – his intensity, passion, and single-mindedness – were the same things causing romantic turmoil. Their fights were like an inferno, a blazing wildfire that scorched a path of destruction in its wake. After these arguments, they fucked the relationship back into existence as fervidly as they fought, a cycle that left the line between love and hate a fuzzy blur.

Until one day Diana strolled into the office and announced that she had taken an assignment in Europe, transfer effective immediately.

He didn't stop her. He barely even looked up from his desk.

In an instant, their relationship was reduced to smoldering ash, a ghost of what it had been at the beginning. Barely recognizable.

Mulder still wondered whether, under different circumstances, he and Diana could have written a different ending. If he hadn't been so preoccupied with the X-Files, could their romantic relationship have flourished? If he hadn't so eagerly blended the professional and the personal, could he have succeeded in both of those aspects of his life? What if he had met Diana later in life, once they had both grown and matured?

Mulder rose from his chair and walked to a file cabinet, still actively avoiding looking at her. "Agent Fowley took me to that plant at great risk to herself where I saw something that you refuse to believe in," Mulder said, frustrated.

He grabbed a file and returned to his chair, still facing away from her. "Saw it again, Scully. And, though it may not say it in her report, Diana saw it too. And no matter what you think, she's certainly not going to go around saying that just because science can't prove it that it isn't true."

His words were meant to hurt, and he succeeded. He glanced up at her and saw the way her eyes had gone glassy, the way she had her arms protectively wrapped around herself.

"I don't doubt what you saw, Mulder. I don't doubt you. I'm willing to believe, but not in a lie and not in the opposite of what I can prove."

When he still wouldn't face her, she concluded with a heavy blow, "It comes down to a matter of trust. I guess it always has."

That certainly got his attention and he forced himself to turn around and look at her.

Trust? She should have punched him in the stomach. It would have hurt less. Trust was the lifeblood of their relationship. Trust was everything.

His heart ached at her words. Scully invoked the one word that instantly ameliorated any conflict between them. His trust in Scully was deep and unwavering. He never doubted her loyalty. Never. She had to know that.

He decided to cut to the chase, to where he thought all this was leading. "You're asking me to make a choice?"

Her or Diana? He would choose Scully. Of course he would. It wasn't fair to him, though, to be forced to prove his loyalty to her after everything they've been through. Not long ago, he went to the ends of the Earth for her. Literally. The ends of the Earth. He would do it all over again if he had to. Scully had his heart in a way Diana never did. A way she never will. That didn't mean he found it acceptable for Scully to issue an ultimatum. Trusting Diana and trusting Scully didn't have to be mutually exclusive. It wasn't that simple.

"I'm asking you to trust my judgment. To trust me," she said.

The more she pushed the issue, the more he wanted to defend Diana. Scully offered him a file.

Primed to dismiss her, he said, "I can't accept that. Not if it refutes what I know to be true."

"Mulder, these are test results. DNA from the nail claw we found matching exactly the DNA from the virus you believe is extraterrestrial."

A lightbulb flickered in his head and all his frustrations with Scully melted away. "That's the connection," he said with wonder, standing from his chair to see the contents of the file.

As soon as she explained the DNA evidence she discovered, showing that the alien virus was part of Gibson's DNA, and, in fact, was part of everyone's DNA, he had a whoosh of understanding. Scully made a breakthrough. While he was running around with Diana, searching for the creature, Scully was doing the actual work to prove his theories.

"So, if that were true, that would mean that Gibson is in some part extraterrestrial," Mulder summarized, his voice full of wonder.

"It would mean that all of us are."

Mulder took the file from her and sat back down at his desk, flipping through the pages of evidence. He didn't understand most of it. He needed Scully's scientific translations to fully process everything. After a few moments, he looked back up at her. She was watching him, her posture stiff, with a sad look in her eyes.

An overwhelming wave of guilt washed over him. He needed to speak up. Thank her. Apologize for making her doubt his loyalty. Still, none of it meant Diana was ever acting in bad faith. Diana believed in the work, and in him, before anyone else did. Her fingerprints were all over the X-Files.

After a tense, silent moment, Scully softly asked, "Can I say something?"

He closed the file and gave her his full attention.

Scully sucked in a nervous breath. "Mulder, I know you think I've been obstinate and, from your point of view, unreasonably suspicious of Diana's intentions."

Mulder had the urge to scoff, make a remark about how it was the understatement of the century, but decided to keep his mouth shut.

She continued, "Despite what you may think, everything I have done has been to help you, to support your claims with hard evidence."

She glanced down at the floor for a moment, breaking their eye contact. She shifted her weight from one leg to another.

Softer still, she said, "I may not remember everything that happened in Antarctica. I'm sorry I don't remember more. But you know me, Mulder. You know I need to be able to touch the proof, hold it in my hands."

There was a part of him that wanted to object, to assert that his experience should be enough for her to believe. The vulnerability in her voice, in her face, stopped him.

"Mulder, I thought my scientific rigor is what you value in me, in our partnership. Those things are a part of me. None of it means that I don't believe in you or, worse, that I'm against you."

The words he confessed to her not long ago echo in his mind: You kept me honest. You made me a whole person.

He meant it then and he still whole-heartedly believed it. Since Diana had been around, his actions did not reflect that sentiment. Not by a long shot. He hadn't been fair to her. He pushed her to be someone she's not. Someone like Diana.

Scully uncrossed her arms, her expression defeated. "I ask you to see this through my eyes. If someone appeared from my past, seemingly out of thin air, and instantly involved themselves in our work, you would be skeptical too. You would question their motives. Of that, I have no doubt."

Imagining an ex-lover of Scully's coming into their lives knocked the wind out of him. In that scenario, he would do everything humanly possible to make that man a distant memory. Her analogy was effective. It instantly reframed the situation in his mind.

He had been a complete ass.

He didn't know what to say. Her directness caught him a bit off-guard. It was rare that he and Scully addressed their feelings so directly. Dancing around their true feelings, leaving things unsaid, was practically woven into the fabric of their relationship.

Finally, he cleared his throat. His voice came out thick and hoarse. "Scully, there's a lot about my past with Diana I haven't told you. It's complicated. I haven't shared everything with you."

"Well," she whispered, her lips pursed, "I wish you would."

Before he had a chance to respond, Scully turned on her heels and walked out of the office.

The click of the door closing made his stomach drop. He wished he could melt into the floor, into a shameful puddle. A violent self-loathing came over him and he abruptly stood. Without an outlet for his balled-up energy, he shoved his desk chair and punched the side of the file cabinet. Acute pain shot up his arm and he cursed, holding his fist.

At that moment, he made a vow to himself. He would not let this relationship flame out until all that's left is ash.