You took the time to memorize me
My fears, my hopes, and dreams
I just like hangin' out with you, all the time
All those times that you didn't leave
It's been occurring to me I'd like to hang out with you, for my whole life
Stay, Stay, Stay – Taylor Swift

IT'S BEST IF WE BOTH STAY
CHAPTER ONE

She's almost shaking as she stares at his door.

What the hell, Kate? You've been here a hundred times. Hell, you lived here for a couple weeks. It's Castle. Your friend. You're having a movie night. That's it.

Except it doesn't feel like a movie night with a friend. It feels like more. The slight hesitation in his invitation to join him, her admission a week ago that her wall is coming down; it feels like they might be crossing that line they've been toeing for years. That line between friends and something more.

And Kate is absolutely terrified.

She brings up his name on her phone, her finger hovering over the call button. She should turn around, go home, tell him she's not feeling well. She's tired; they caught a rough case, the ones with kids or teenagers always are, and he's seen how they can affect her. Especially when there's a delay. Forensics had been backed up, so the results on DNA found at the scene hadn't come back yet.

The door swings open before she can make her move, though, revealing Castle in jeans and a blue v-neck sweater that brings out his eyes, and holy shit he looks hot. She rarely sees him in sweaters anymore, since he opts instead for crisp button-downs. While she's glad the arrogant man-child from the first couple years is gone, sometimes she misses the casual look he would sport.

"Beckett!" Castle's giving her a wide grin, which morphs into a smirk when he glances down at her phone to see his own face smiling up at him. He cocks his eyebrow at her, amused. "Lemme guess. You were about to turn around and call me while you were leaving, saying that you're tired and should probably just rest."

Kate quickly locks the screen and shoves her phone back into the pocket of her jeans. "No," she argues, but there's no force behind it, and besides, he knows her tells. He'll know she's lying.

Castle steps to the side. "Liar," he teases. "Come on in. I just finished up the popcorn, I got some M&Ms and gummy bears. What would you like to drink? Wine, beer, I can make you something?"

Kate toes off her sneakers at the door, shoving her hands in her pockets as she follows him into the kitchen. "Um, water, I think. For now." She gives him a smile when he hands her a glass. "Thanks, Castle. How was graduation, Alexis's speech?"

"She was amazing, no surprise there." Castle puffs a little with pride. "She'd probably give an encore performance if you ask."

Kate takes a drink of her water with a smile. "Yeah, I'd love to hear it."

"Great. Shall we?" Castle takes a beer for himself and leads her into a room she hasn't been in before. He leads her through his office, and-

Of course he has a secret room that he's converted into a theatre. Sure, why the hell not?

It's small and cozy, a couch on one end of the room and a big-screen TV on the other. He has blankets piled on one of the ottomans in front of the couch, and there are pillows strewn all over the floor. She can't help but roll her eyes at the whole set-up; the nine-year-old on a sugar rush is still in him somewhere.

But who is she kidding? She loves that about him.

"Make yourself comfortable," says Castle, sweeping his arm towards the couch. "I'll be right back."

By the time he comes back, juggling the popcorn and candy, as well as two smaller bowls, Kate's leaning up against one of the arms of the couch, her toes tucked between the cushions and her head leaning against the cushions, eyes closed.

She opens her eyes when Castle sits across from her, a cushion between them, and gives him an embarrassed smile. "Sorry," she says quietly.

Castle hands her one of the smaller bowls and sets the snacks between them. "Are you sure you're up for this, Beckett? I know we're in the middle of that case, and it's been a long day…"

"No, no, I'm fine." Kate shifts, tucking her feet underneath her instead. "This is just a super comfortable couch."

Castle grabs a blanket and hands it to her. "Well, don't feel bad if you fall asleep," he says. "But you should know that I make a very nice pillow," he adds with a wink.

Kate rolls her eyes, tucking the blanket around her. "Just start the movie, Castle."

She starts to fade 20 minutes into the movie. She's warm under the blanket and the couch is a plush leather, much more comfortable than her own, which she'd collapsed on the previous night. She covers a yawn, then another, and finally when she barely catches the third Castle speaks up.

"Do you want to stop?" he asks quietly, pausing the movie.

Kate waves a hand as if to dismiss the thought. "No, no, it's fine. I'm fine." She ignores the pointed look he gives her, keeping her eyes glued on the screen in front of them even as he moves the food to the floor. What the hell is he doing?

Castle shifts so he's facing her, one leg curled on the couch. "Kate," he says quietly, tenderly, "you don't have to stay. We can do this another night."

She's shaking her head by the time he finishes his sentence. "Nope, we made a date."

As soon as the word comes out she freezes, eyes wide.

Shit.

They just stare at each other for a few moments, or hours, or days. She can see the desire in his eyes even from where she's sitting, the light from the TV reflecting in his dilated pupils so his eyes look wild, even a little dangerous. Like he wants to say "to hell with it" and just ravish her.

As if he knows what she's thinking, Castle's gaze flickers from her eyes to her mouth and back again.

"Is-" It comes out gruff and he has to clear his throat. "So, this is a date?" His voice is low and husky, laced with something that sounds suspiciously like desire.

The corner of Kate's mouth lifts in a half-smile. "Depends."

"On what?"

What are you doing, Kate?

"On whether or not you want it to be."

Castle reaches his arm towards her along the back of the couch, their outstretched hands not quite touching. "I think I've made my intentions clear," he says slowly, his eyes on the space between their fingers. "You told me once about the wall you built inside, and you recently you said that it's coming down." He shifts his gaze to look in her eyes again. "I have every intention of bulldozing the rest of that wall until it feels like it never existed."

Kate nods, her eyes moving to their hands. She takes a deep breath and reaches out to brush her fingers against his, and he turns his hand over and curls their fingers together.

"I'm scared," she whispers, ignoring the rush of desire that runs through her blood at the contact.

Castle leans forward slightly so he can take more of her hand. "Of what?"

After a long minute, she finally meets his eyes again, her vision blurred with unshed tears. "Of me. Of us. This. I'll mess up, Castle. I'll do something stupid and fuck this up, and I'll lose you, and you're my partner, my best friend, and I don't know what I'd do without you."

"Hey." Castle squeezes her hand to interrupt. "I'm not going anywhere. I'll mess up too, but we'll figure it out. If we can survive a freezer and a serial killer and a bullet to the chest, we can survive a relationship."

Kate involuntarily curls her free hand to her chest, to the scar that caused so much pain for both of them, physical and emotional alike. Her voice shakes when she speaks again. "What if we don't?"

"What if we never try?"

She nods once, almost as if to seal her decision, and tugs slightly on his hand. She uses it as leverage to rise up on her knees and shuffle to his side of the couch.

"I'd like to try."

Letting go of his hand, she trails hers up his arm to the back of his neck, her other meeting it, and she kneels directly in front of him. Her fingers play with the fine hairs at his nape as she studies his face, the way his eyes flutter close at her touch. He obviously wants this, but the last few weeks, how withdrawn he's been...

Oh. Oh.

"You know," she blurts out suddenly, the final piece of the puzzle clicking into place. "You know I heard you when I got shot. That's why you were upset, why you pulled back. You heard...but when?"

She's only inches from him, her eyes studying when he opens his. He holds her gaze until she finally gasps, the final piece clicking into place.

"That bombing case," she whispers. "Oh, God, Castle. That's why you left in the middle of the day. You heard the interrogation."

He just nods.

Kate shakes her head at herself. "I'm so sorry, Rick. I can't even tell you how sorry I am. You must have thought I didn't care. Shit. I really messed up." She moves her hands to his shoulders. "What can I do? How can I make this up to you?"

He's shaking his head before she finishes her question. "Nothing," he assures her. "You're here. That's enough for me right now. As long as I know you do actually want this, that you're working towards it, I'm willing to wait until you're ready."

"You're amazing," Kate says quietly, a smile tugging at her lips. "I don't deserve you."

Castle finally brings his hands up to bracket her waist. "No, Kate," he whispers, shaking his head, his thumbs brushing against her ribs. "I don't deserve you."

Kate pauses briefly before leaning forward to capture his lips with hers. It's soft initially, hesitant, but before long she slicks her tongue against his lips and he willingly opens for her. She kisses him slowly and deeply, acquainting herself with his taste, and Kate knows that she doesn't want anyone else.

She wants to spend the rest of her life with this man.

She pulls away before long, when his hands are dangerously close to the hem of her sweater and hers are itching to feel his skin. She searches his face when she pulls back, and his eyes are still closed, like he's trying to memorize the kiss they just shared.

Finally, Castle opens his eyes with a smile on his face. "That was..." He grasps for the right words.

"Amazing?" Kate supplies, reminding them both of the first kiss they'd shared, over a year before as an undercover diversion.

Castle quirks an eyebrow. "Epic also comes to mind."

"Epic, huh? Just wait until I get you in bed. You don't know what epic is yet," she teases.

Castle grins and starts to lean in when she suddenly yawns. "Well, I've never had that reaction to a kiss."

"Shut up, Castle," Kate says lightly, nudging his shoulder. "Look, I want this. I really, really want this."

"Me too." He sees the regret in her eyes. "But we're in the middle of a case."

Kate nods. "When we do this, like do this this-" she waves her hand between them, "-I don't want to be rushing off to the precinct in the morning because forensics came back. I want to be able to enjoy myself. Enjoy you. Have a lazy morning, you know? Am I making sense?"

Castle reaches up and tucks an errant piece of hair behind her ear. "You're making perfect sense," he says quietly, brushing his thumb under her eye, at the edge of the dark circle underneath. "After the case? Try this date thing again?"

Kate gets off the couch and extends her hand, pulling him up to her when he takes it. She locks her arms around his waist and leans back to look up at him. "Absolutely."

She helps him clean up, taking the food back to the kitchen while he folds the blankets they'd used and puts the movie away. Kate gets lost in her thoughts as she washes the bowls and sets them out to dry, marveling at how comfortable she feels here. She knows where everything is; it's warm and inviting, the fireplace going almost nonstop during the fall and winter. Even now, with summer approaching, it's the perfect temperature inside. She loves being here. It's relaxing, and...home.

It feels like home.

She startles when Castle appears at her side to dry the bowls, and he smiles in apology. "I can finish up," he offers. "You go home, get some sleep. Better yet, why don't you stay here? You're always welcome."

Kate shakes her head. "If I stay here we won't be doing a lot of sleeping," she admits, her cheeks flushing. She rinses the pot he'd used for the popcorn and hands it to him. "After the case."

"After the case." He dries it and sets it aside to finish walking her to the door. "Thanks for helping clean up."

She slips her shoes back on, using his shoulder for leverage, trying to ignore the flash of desire at the feel of his muscles under her fingers. Simmer down, Beckett. She pats her pockets: keys and phone, check. "Thank you for understanding," she says quietly, looking up at him through her lashes.

Castle takes her hands and leans down to give her a soft kiss. It's just a meeting of the lips, nothing more, and he pulls away before she can surge forward for more. "Always, Kate. See you tomorrow."

"Good night, Castle."

A/N: Some ideas are born out of Twitter conversations. Some are prompted. This is a combination of both. This fic is for Ally, Callie, Cathey, and Lou, who heavily encouraged me to write this. So, ladies, this is for you.

So many thanks to Callie (whatifellinlovewith) for betaing this and putting up with my insecurities, and also for the awesome cover art that I am absolutely in love with.