Watching
There was something about Temperance Brennan. He found that out the day he met her, when he walked into the lab expecting a typical Squint and instead discovered a beautiful woman who possessed the ability to make him feel like an idiot with a single look.
He had gotten to know her well, arguably better than anyone else. He knew when she was annoyed by the way her eyes flashed, and that when her lip quirked a certain way, she was confused and he needed to explain something. When she was lying, she couldn't look him in the eye, but when she thought she was right, he couldn't get her to look away. Yes, he knew her, but so much about her was still a mystery.
But he planned on figuring it all out. That was why he watched.
His eyes were glued to her back as she examined remains, to the way her hand moved to accentuate a point when she talked on the phone. Even when she was yelling at him, he couldn't help but study the way her lips moved.
And he thought he did a pretty good job hiding it, too, at least a good enough one that she never caught on. Until she did.
They were in the diner after solving a case, and she had just popped a fry into her mouth when she glanced up and commented, "You've been staring at me for nearly five minutes, Booth."
He tensed. "No, I haven't."
Ignoring his stammered denial, she pressed, "Why?"
"Um…" Caught off guard, he had trouble thinking of a sufficient response. And she waited. "I was making sure you didn't steal any of my fries. You always do that."
She nodded slowly, obviously skeptical, then took a sip of her drink. "You could just take a picture." A smirk. "It'll last longer."
So he pulled out his phone and pressed the camera button, capturing her image just before her expression changed from amusement to shock. "To commemorate you actually getting that expression right," he offered, turning the phone so she could see. She shook her head and threw a fry at him.
Later that night he stared at that picture. And while he was beginning to fear he would never fully understand his partner, he had now realized a very important fact about himself. He was in love with her.
That was why he watched.