A/N: There are a few spoilers here, but I have taken some creative liberties as well. The objective here an exploration of the worst-case scenario we can imagine for this pair, irregardless of what we may or may not know about the finale.
She met the standards of a superior mate, evolutionarily speaking. The woman had symmetrical and expressive features, large, rounded eyes, a clear complexion and lengthy, shiny hair. She was also clever, educated, dynamically tempered- at once feisty and agreeable- and had her own means but knew when to yield to Booth's desire to provide for her. She could appreciate why Booth had affection for her.
What she did not appreciate was the seating arrangements at Angela and Hodgin's wedding. Their table of eight could have been better planned: Booth and Dr. Bryar were uncomfortably centered in the natural drift of her gaze throughout dinner. Daisy and Sweets waxed nauseatingly about love. Cam and Dr. Lidner shared the enthusiasm of a new relationship. And Andrew- she just did the best she could to pretend to enjoy his company, despite how inferior she had grown to find him. Only his statute and career status remained pleasing to him. His humor had become grating, and his enthusiasm to indulge her biological urges, of which she had none directed towards him, wore at her resolve. Nevertheless, she would maintain her composure, and danced with him awkwardly in acknowledgment of her social obligations. It was only out of a desire to maintain her own dignity that she directed her wandering eyes past Booth and Dr. Bryar and towards the happy couple.
Little, however, could dull the irrational pang of jealousy and regret. She unyieldingly understood that she had made the right decision. There was too much uncertainty in his proposals, there were no "rules of the game,"- no guarantee of the cooperation required for success. While Hodgins had been right to point out to her that game theory was not the appropriate tool for relationship analysis, and that she had introduced damaging uncertainty into her partnership with her own defection, she knew that this outcome was an ultimate certainty. By introducing it early, she hoped she would have enough turns to reverse the pattern. Judging by the way Booth chose to defect now by lasciviously applying his affections for Dr. Bryar in her face while Andrew stepped on her toes, it appeared she may have miscalculated the duration of her opportunity.
Fortunately, or unfortunately, Brennan knew that she was in control of the situation. When she had been invited to the Australopithecus dig in South Africa, she knew she would be unable to turn it down. Not only was it a chance of a lifetime, but it was an opportunity to end a game that was torturing them both. By controlling the last turn, she could take a small victory in the fact that she, too, was moving on. This was a small consolation as she watched Dr. Bryar and Booth get into a cab, visibly inebriated, amorous and absorbed in one another.
Monday Afternoon, The Jeffersonian
Brennan paged through the dissertation of one of her graduate students- her red pen wielded like a small dagger, supplying enough cutaneous injuries that bled disappointment all of the work. She expected better from a student that would be required to defend soon, but she tried to balance her disappointment with the knowledge that it was somewhat self-inflicted: the student would have less time to prepare because her decision to go to South Africa.
"Bones, you got a minute?"
Brennan looked up towards the voice to find Booth leaning in the frame of the door and hands inserted into his pockets with more determination than average. He had been laconic lately, limiting casual conversation where it might drift towards too-familiar or uncomfortable subjects, late nights with paperwork and Thai food, lunch-time case brainstorm sessions and celebratory drinks with the team. This is not to suggest that he been unfriendly, or that what interactions they still did have deviated very much from the established norm- only that they just had fewer of them.
"Sure, Booth. Do we have a case?" she inquired as she dropped her pen into the organizer. She grabbed her bag out of habit and set it on the desk, indicating that she was prepared to go.
He shook his head, "No. I need to talk to you about something," he frowned briefly, "But we shouldn't do it here. The diner, maybe? You hungry?"
Brennan looked at him curiously, allowing apprehension to flicker over her face only briefly. "I could be persuaded to eat some fruit salad. I have been meaning to discuss something with you as well." After collecting the documents on her desk into a neat pile and shouldering her bag, she looked up and smiled at him, hiding the anxiety boiling in her stomach. "Let's go."
Brennan pushed around the cantaloupe in her fruit salad in search of the grapes. She was aware of the necessity of calories, both from the persistent grumbling of her stomach and the general malaise she had been experiencing since that night put a dent in the only factor of normalcy in her erratic schedule. However , she was unable to indulge her body in anything but a sad attempt at eating. She pretended not to notice that Booth was doing little more than picking at his fries. Emboldened by their mutual misery, she reached over to steal one from his plate.
He looked up at her wearing a matching smile of endearment, haunted by the specter of grief and worry. "What's on your mind, Bones?"
"I have some exciting news, but you should go first."
Booth paused like he might insist she continue, but he yielded. "I am going to be taking a leave of absence for a year," he looked back down towards his fries at her unnaturally stoic expression, "The Rangers need me to train snipers."
Rationally, she knew that staring at the top of his head would not allow her to read his mind, so she waited until he looked up at her again. His eyes were more elucidating. "Why? What about the balance? What about Parker? And Dr. Bryar?" Silently, she asked, What about me?
"You know why. Parker will be fine," he responded tersely, leaning back against the booth, "Tell me about your exciting news," he pressed unenthusiastically.
Brennan couldn't help but feel taken aback by his decision. He was making his final defection, not just at her own expense, but at the expense of himself, and his son, and their partnership, and…She found it unusually difficult to maintain an organized stream of thoughts. His decision was irrational, even from his perspective. She was at once confused, frustrated and enraged. She felt abandoned. She felt like he was blaming her because he had to demand what he knew she couldn't give. She knew that she had hurt him, and that their injuries were not equivalent, but he had placed them on a level plane now- their scores were tied, and she held the last card.
"I've been invited to participate in a hominid dig in South Africa," she informed him flatly, reaching for her glass of water, "For a year." She punctuated her statement with a swallow of her ice water, "And I am taking Ms. Wicks- she and Dr. Sweets will be postponing their wedding date due to the significance of this opportunity for us both. "
Booth was less adept at stoicism, and his reaction- a furrowed brow, a cast of disappointment in his eyes, a sigh of frustration, the purposefulness in his mastication- "Sweets must be thrilled," he replied with sarcasm.
"Actually, he is disappointed in Ms. Wicks decision. However, he understands how much this means to her, and plans to visit frequently." She was not hesitant to present the subtext in the form of a bitter tone.
"Congratulations, then," he offered her with as much sincerity as he could muster, and tossed several bills on the table, "When do you leave?" he asked, pulling on his coat.
"Next Wednesday. Yourself?" The lilt in her voice was exceedingly polite, and the irritation she had intended to muster was visible."
"In a month. I thought I'd provide you with the courtesy to interview a new partner. " He looked down, incredulous, wiping his jaw, "I assume you informed the bureau?"
Brennan nodded, gathering her own belongings, "Several weeks ago. I expect that is the source of the decline in cases we have been assigned this week. There would be insufficient time for me to contribute my expertise so close to my departure."
Booth's body language became increasingly agitated at her reply, and then relaxed altogether. He nodded, watching her with uncomfortable attentiveness. Her victory felt sour. "Have a nice trip, Bones," he finally conceded with a hand resting against the side of her shoulder. He stepped forward, like he might hug her, and she leaned in like she might accept it. Her arm burned at his touch. Her body raged for the oxytocin, the dopamine, the vasopressin response that would relieve them both. Instead, he dropped his arm, and left the diner.
They had missed their moment, and they continued to punish each other.