Sweets just happened to be looking out the window—and look, he was not a creeper or stalking Booth and Brennan or in any way acting inappropriately; he just happened to be looking out at the night sky and maybe a little bit downward—when he saw two people who looked remarkably like Booth and Brennan kiss. "Kiss" was, perhaps, not the right word, because that was a broad umbrella term that included pecks on the cheek and chaste hellos and the drunken press of a frat brother's lips who vehemently denied that he meant it like that, but all the same really loved you, man, whereas this? This was passion and fire and dams bursting.
Finally, Sweets thought, and his emotions were some strange mix of relief and joy and longing.
Then they pulled apart and talked for a while, and when they walked away and into the night, shoulders bumping, that was not the body language of two people going home together. Sweets thought, maybe it's not them. Then, because he could be honest if only with himself, he acknowledged that not only was it totally them, they'd found some new and unexpected way to mess it up.
Because it was late, and Sweets had just suffered a devastating loss (his book! totally his book), and the pot of coffee was right there, Sweets decided to drown his pain in coffee and flow charts. That they revolved around Brennan and Booth was only to be expected, because they were the subjects of his study. This was just a way to reacquaint himself with the basics and work out some new theories. It was all very academic.
"—And that is why you and Dr. Brennan have to give it another shot." Sweets concluded, feeling a bit wild-eyed, but in his defense, Booth had asked, though he'd probably expected an answer along the lines of "squint stuff" rather than a twelve minute diatribe on how he and Brennan were probably the psychological equivalent of soul mates.
"What does MFEO mean?" Brennan asked Booth, staring at the last box on the flow chart.
Booth cleared his throat awkwardly. "Made for each other."
"Which you are," Sweets said, because he was nearly shaking from the three pots of coffee (he hadn't been done when he'd finished the first and needed to make more to keep going, because those charts weren't going to finish themselves, and left to their own devices, Booth and Brennan's relationship was conclusively doomed, as were, in all probability, Sweets's objectivity and academic career at this point) and he really could not stop himself.
"It is very logical," Brennan agreed, and her gaze, when it landed on Booth, was one of reconsideration.
"Thank you," Sweets said.
"I put my heart on the line, and you tell me you're a scientist," Booth said disbelievingly, "but he pulls out a few charts and a Venn diagram and suddenly you're on board?"
"I am a scientist," Brennan said.
"You—" Booth said, and see! Right there! Left to their own devices, ruination, just like Sweets's hopes of academic well-being.
"Just go with it," Sweets interjected hurriedly.
To his relief, Booth did, pulling Brennan in to kiss her right there in Sweets's office, all passion and fire and bursting dams once more. When they pulled apart, Brennan looked at Sweets, and Sweets tried to project with every iota of his being, DO NOT RUIN IT THIS TIME. To his surprise, she smiled and said, "You know what's even more stable, Booth?"
"What?" Booth asked dazedly.
"What?" Booth said again, and Sweets honestly couldn't tell if it was general confusion brought on by the kiss—still not the right word—or if it was confusion specific to Brennan's statement. If the latter, Sweets was right there with him.
"Polyamorous relationships actually have a higher than socially expected success rate," Brennan said. "In Tibet—" She stopped, having obviously decided that Booth was not in a place where he'd appreciate the lecture and Sweets—wasn't really, either.
"What?" Sweets asked weakly, clutching his flow chart like a throw pillow to his chest.
Booth recovered first. "Really?"
"Really," Brennan said and nodded decisively.
"Don't tell me we need to draw you a flow chart, too," Booth said, advancing on Sweets's position.
"I don't believe that will be necessary," Brennan said, right behind him. "Dr. Sweets has always been vulnerable to less logical persuasion. I believe a practical demonstration will suffice."
Sweets found—first Booth, then Brennan, and those were definitely not just kisses—this to be very much the truth.