A/N: Enjoy!

Disclaimer: sighs Nope, I don't own Bones.

A Constant Variable

To Temperance Brennan's delighted satisfaction, the day so far had unfolded in a slow and quiet manner. It was not unlike any other Thursday, in fact, and this pleased Brennan to no end.

She had purposefully come into the Jeffersonian early this morning, aiming to avoid anyone and everyone she did not need to see. No new cases had presented themselves and there had been no need to work with her team today, so she had not ventured out of the safe confinement her office held. In there, she had done paperwork for the majority of the day. Of course that hadn't stopped Zach, Angela and Hodgins from popping in to wish her a "happy birthday". However their stops had been quick, with the exception of Angela who had come in to give her friend a hug, a card, and a gift along with her birthday wishes.

Now, Brennan sat flipping absentmindedly through an old text book that she still found quite interesting and informative. Although, her mind was wandering and she couldn't help but glance at the clock trying to gauge how many hours she should remain in her office. She wanted to leave as soon as possible, but she didn't want to raise any suspicions among her colleagues. She knew that she normally went home at abnormally late hours in the evening, and that if she went home at six, people would jump to the conclusion that something was wrong.

That was the last thing Brennan wanted; to draw attention to herself. This day was not unlike the day before or the day that lay ahead, it just happened to be the day she was born on. However, babies were being born at every minute of every day around the world, so really today was nothing special. That was what Brennan wanted to make clear to people; that since today meant next to nothing to her, it should mean even less to everyone else.

A soft knock jolted Brennan out of her inner thoughts. Looking up she sighed, she knew he would come today. She wanted him to ignore her birthday just as she wanted everyone else to; but another part of her wanted to spend the entire day with him, just relaxing and being in each other's presence.

Scoffing out loud at her own thoughts, Brennan allowed him to enter, "come in Booth."

The doorknob turned and a brown haired brown eyed man slowly pushed the door open, stepped into the room and quietly shut the door behind him. A grin played on his lips, "how'd ya know it was me Bones?"

Brennan smiled slightly, "lucky guess."

Booth's smile widened, "well you were right!"

"As I usually am," Brennan replied. Her smile then dropped, "why are you here Booth? Do we have a case?"

"A case? No… try again!" Booth teased.

Brennan shot him a sharp look.

Holding up his hands in defence, Booth grinned. "Jeez Bones, did you forget your own birthday? That's why I'm here!"

Brennan shook her head and looked back down at her text book. "No, I didn't forget it, but I wish everyone else would." She looked back into his eyes, "you didn't have to get me anything Booth. I told you not to."

"Whoa! Get you anything? Who said anything about getting you a gift?! Can't a guy just wish a girl happy birthday anymore?" His eyes twinkled.

Brennan couldn't help but smile at the expression on his face and at the playfulness in his eyes. "Yes, he can. I just presumed you had brought a gift, or driven over here to do more than just give me birthday wishes."

"Well I would do more if I could, but you…" Booth mumbled.

"What?"

"Nothing," Booth replied more audibly, with a slight flush to his cheeks. "Technically I did get you a gift, but it was hard to wrap and, well, it didn't cost anything." Again a grin spread across his face.

Brennan tilted her head, "I don't understand what you're trying to say. However, you didn't have to get me a gift, regardless of the price or its ability to be wrapped."

Booth sighed, "I think you should come take a seat on the couch because it might take a while for me to explain the, uh, reasoning behind my gift."

Narrowing her eyes in suspicion, Brennan slowly got up and went to sit down on the couch. "I have a while," she replied.

Booth nodded, sat down beside her, and turned to face her. His eyes were soft, but his face was now serious. "Bones, I had no idea what to get you for your birthday - "

"You didn't have to get me anything!" Brennan interrupted.

"Hey!" Booth cried. "This is my time to talk, so no interrupting or speaking until I'm finished, okay? Good. As I was saying, I had no idea what to get you for your birthday. My mind of course jumped to all the usual birthday gifts, chocolate, jewellery, gift cards. But I didn't think any of that suited you, or our relationship."

Brennan sucked in a considerable amount of air at his last three words. "Boot-"

"Ah, ah, ah," Booth held up a hand, "let me continue." But he was smiling at the reaction that had arisen from her. "I then thought of the unusual things, such as textbooks and human remains. And while those suited you, they still didn't suit our relationship. So I continued to think of what you would want or need for your birthday. Then my mind began to drift to your childhood because that's when the best birthday memories are created."

Brennan looked away from Booth, the thought of her childhood birthdays stinging in her mind.

Booth noticed this, but carried on talking. He couldn't waver now, no matter how much he wanted to envelope her in his arms. "But then I realised that those were probably when your worst birthday memories were created; and that if you had any good ones, you had most likely tried to suppress them for fear of being disappointed on another birthday. I then understood why you went into seclusion every year on the day you were born."

"I hate psychology." Brennan sniffed.

"I know," Booth said in a soft caring voice. "But you have to hear all of this to understand my gift. The reason your birthdays have left a lot to be desired, is because no one in your life has been there for every single one of your special days. And for that, I'm sorry. I'm sorry you've felt alone on your birthdays and on every day of the year. Truly Temperance, I am sorry."

Booth's eyes searched for Brennan's, but he was dismayed to see that tears were brimming in her eyes. "You have nothing to be sorry for Booth."

"But I want to say I'm sorry," Booth replied quietly. "I want to make you feel better."

Brennan's heart swelled with emotions as the tears spilled down her cheeks.

"This," Booth forged on while still looking carefully at Brennan, "is where my gift comes in." He reached down to wipe her tears with his thumbs. Brennan looked up into his familiar protective gaze, and shivers shot down her spine as he wiped her cheeks.

"Thanks." His hands felt like fire on her face, but it was the nicest feeling that she had felt in a while.

Booth pulled back his hands, smiled warmly and took a deep breath. "Temperance, my birthday gift to you, is me."

Brennan looked at him startled, her blue eyes searching his. "Your gift to me is you?"

Booth nodded. "Yes, me."

Brennan once again tilted her head. "I don't understand."

Booth looked into her eyes. "Really? You don't?"

Brennan turned her head back and forth slightly, but tears were coming back to her eyes, for somehow she did know what he meant.

"From now on," Booth started, "I'm going to be the one that will always be there for you. You've never had that type of person before, and I'm sorry I couldn't have been that person for your entire life. But from now on, I will be. Not just on your birthday, but on every day of the year. Things will change around you, friends and people will come and go, but I will always be there for you. No matter what happens, I will remain the constant variable in your life." He finished.

Brennan was crying again. Crying for all the people that had left her behind and crying because Booth was willing to never leave her behind. She couldn't speak she was crying so hard. Caught in the moment, she overlooked the fact that Booth might not keep his promise, and throwing caution to the wind, she flung her arms around his neck.

Booth was surprised by her sudden show of affection, but he didn't object to it in the least. Instead he returned her hug immediately, wrapping his arms around her waste and pulling her close.

They melded together and heat danced of them, twirling around their bodies. Both could feel the other's heartbeat as it became one with their own.

Brennan never wanted to leave Booth's embrace. It was so strong, so safe, so loving. Booth was just as unwilling to let go. With Brennan in his arms he felt as though she belonged to him, the she was his Bones.

Carefully, without any sudden movements, Brennan leaned back to look into Booth's eyes. She wanted to search them for the truth that hopefully lay behind his words. Booth gently loosened his grip on her waste and looked down into her eyes; knowing that she was looking for the certainty in his promise.

Brennan's face was flushed, her cheeks were damp and her normally ice cold eyes had melted into a cool blue. Booth's own eyes were now smouldering into hers. She smiled at him and he knew that she had found what she was looking for.

Booth smiled back. "You like your gift then?"

"I love it."

Booth nodded and slowly leaned down towards Brennan capturing her lips with his in a tender kiss. Brennan snaked her arms up around his neck and kissed him back. It was a sweet soft kiss, which spoke of their true love for one another. Brennan was surprised at how much she had been longing for this and at how long she had been waiting for it.

Booth tugged her closer and murmured against her lips. "Funny, your gift feels the same about you."

Brennan laughed softly "good." Then she kissed him again, but this time the kiss was not only filled with love but with passion and lust. Their mouths seemed to fit together perfectly and Booth and Brennan couldn't seem to get enough of each other. Brennan was reluctant when she finally had to go up for air.

"Happy birthday Bones," Booth said grinning.

"Thank you," Brennan replied breathlessly a small smile playing on her lips. "For everything Booth, you have no idea how much it means to me."

"It's my promise and pleasure," he replied as he kissed her once again.