"Maybe it's all down to the thought of her,
Maybe it's all down to the loss we learned,
Knew for a long time for all it's worth...
I loved you.
Does that mean nothing to you now?
I loved you.
Get me back on homely ground"

-Moments Passed, Dermot Kennedy

Castle runs a hand through his hair, dispelling the flakes of snow clinging to the strands as he enters the church. The warmth of the building embraces him, attempts to soothe the chill from his bones, but winter clings to the skin beneath his coat. He still doesn't know if he's making the right decision or his greatest mistake yet, but it's too late now. He's weaving through the crowd of guests filing into the church and chattering in the lobby, following the directions that a woman named Lanie gave him.

"Straight down the right corridor, there'll be a door at the end of the hall. Kate should be finished getting ready in there by now," she informed him, nodding towards his destination with a skeptical look on her face and an eyebrow raised high. "You sure you're in the right place, Mr. Castle? Beckett never mentioned inviting a best-selling author."

"It's kind of a surprise," he explained in return, throwing Lanie his most charming smile to hide his nerves. It worked long enough for him to take her instructed path before anyone else could recognize him.

But now, Rick hesitates outside the elegant doorway, his fingers balanced atop the golden curve of a handle and his heart in his throat.

It's been so long since he's seen her and he longs to see her again, but what if she has no desire to see him? What if the sight of him brings back nothing but the pain of that last day spent with her?

But he made a promise and he's always been a man of his word. If Kate asks him to leave, he will, but at least he would leave knowing he honored her father's wishes.

Rick curls his fingers around the handle, slowly eases the door open.

He slips inside the room and almost chokes at the sight of her.

Stunning. So stunning, like a goddess illuminating the room. He's left speechless, a specter in awe of witnessing Kate Beckett assess herself in front of the full-length mirror. The sweep of her gaze down her body is critical, the slender lengths of her fingers fidget with the skirt of her dress, tangling in the tendrils of hair framing her face - she looks restless, riddled with unease, but gorgeous.

She's even more gorgeous than he remembered.

The last thought, its accompanying adjective, must have escaped past his lips, because Kate startles. Her eyes rise to meet his in the mirror, widening the second they land on him.

"Rick?"

"Hey," he responds, stupidly, adding a ridiculous little wave of his hand.

"What're you…" Her voice trails, her eyes holding onto his in the glass. Her reflection allows him to see the moment clarity spreads soft and golden through her gaze. "How did you find out I was getting married?"

Rick shrugs, straightening the lapels of his suit jacket. "Your Aunt Theresa messaged me on Facebook."

A surprised laugh flutters from her lips, her fingers rising to catch it. But it doesn't stop the smile, real and glimmering with a glimpse of teeth. "You're not supposed to be in here."

"Why?" Rick challenges, easing the door shut behind him, silencing the excited murmurs of the crowd down the hallway and congregating in the main chapel.

"You're not supposed to see the bride before she walks down the aisle," she tosses back, halfheartedly returning to her examination in the mirror, her hands ceaseless as they smooth over the tulle of her dress.

"That's a rule for the groom," he informs her, his tongue heavy around the correction, his teeth biting back the urge to tell her the truth, to lay it all out at her feet.

He should be the one marrying her today.

It was always supposed to be him.

"I'm just the guy walking you down the aisle."

Kate's hands slow to a stop over her hipbones. She finally turns away from the mirror, allows him a perfect view of her in her wedding dress.

"Kate," he whispers, willing his throat not to tighten around the simple syllable of her name. "You're… breathtaking."

Her lips part, an unsteady little exhale slipping past, but she shakes her head, stepping away from the middle of her dressing room, towards him instead. "Walking me down the aisle… you say that like it's nothing."

"It's just-"

"You kept your promise," she murmurs, lowering her eyes, swallowing hard. "It would mean a lot to him, to both of them."

His heart clenches at the mention of her parents, their absence.

He met the Becketts after years of travelling around the country with his mother, landing in New York City when he was eleven years old, moving into the same apartment building as the two lawyers and their clever nine-year-old daughter, Katie.

She hated him in the beginning, ignoring him every time Martha requested Johanna watch him for the evening while his mother headed off to rehearsals. He can still remember the arguments he would hear a young Katherine Beckett having with her mother about how it was an 'unlawful play date', can still recall how she sat at the dining table with him, unwillingly scribbling in coloring books and learning to share her Legos so they could build castles together. How eventually she grew to accept his presence, started to welcome it after a few weeks.

By the end of that first summer, he was her best friend and she was his. He held the title throughout the years of grade school, despite the teasing they both received for it and the difficulties their two-year age gap would sometimes provide. He always saw her after school, walked home with her, and usually did his homework in the Becketts' living room with Kate at his side and one of her parents in the kitchen making dinner.

College was never a priority for him, but Kate encouraged the idea, coaxing him with the advantage it could serve to his writing. Along with the daydream of spending another few years with her if he was able to make it into the school of her choice.

As if he was going to say no to the idea of a co-ed Beckett.

At eighteen, he was accepted into NYU and Kate wasn't far behind, graduating a year early, joining him in classes and making their parents proud.

He misses those days.

Her mother was killed after that first year and her life fell apart, spiraling off course. He never blamed her for drowning in the darkness, still can't imagine ever resenting her for it, but with her mother's death went their friendship.

"I need to do this alone," she told him on the steps of the church after her mother's funeral, dressed in black with tears glittering in eyes that no longer lit up for him. They turned to lifeless, dark brown trenches of her grief on display.

"Do what alone?" he demanded, moving in to touch her, but Kate took an abrupt step back.

"Deal with it," she murmured, squaring her jaw, the line of bone sharp enough to cut.

"But Kate, I'm… you're my best friend. This - we can get through it together, like always."

He thinks he inadvertently caused the cracks in her heart to splinter deeper that bitter January day, remembers the horror that welled up in his chest when the tears in her eyes started to fall.

"Kate," he tried again, his own heart beginning to shrivel up in his chest.

"I can't be your best friend," she grinded out, trying so hard to wear a mask of indifference, to be strong. "I can't - can't be anything. Not until I - I have to find her killer. It's all that matters. All I have room for."

"But I - I love you," he managed, the words coming out all strangled and wrong, so very wrong.

She choked on a sob that tore him to pieces.

"I'm sorry, Rick. I'm so sorry." And then she stepped up to him, kissed the corner of his mouth and whispered one last apology into his skin before retreating, leaving him to freeze.

That was the last conversation he ever had with his former best friend. Until he learned of her engagement to a prestigious, square-jawed FBI agent and, through the burn of acid spilling inside his chest, he remembered the promise he made to Jim Beckett.

"Make me a promise, son," Jim mumbled, tracking him down only a handful of months after Johanna Beckett's funeral, meeting with him in Kate's favorite diner. He already knew then that whatever promise Jim Beckett would ask him to make, he would swear to. Because this was a man who was the father he never had, always wanted, and he owed it to him. Despite the liquor he could smell laced through the words. "I know my daughter hurt you, that she's too wounded, too… broken right now to see it, but she needs you. I - I can't be there for her, not anymore. I've failed her and just… I was thinking, she's going to get married one day-"

Castle pursed his lips, protests already bubbling in his chest. "Jim-"

"I'm hoping it'll be to you," Jim sighed, so wistful and wasted, already fading away in front of Rick's eyes. "But if for some reason it isn't, be the one to give her away for me."

"No," Castle croaked, clearing his throat, but it was no good. The lump lodged within his trachea was a permanent one. "You'll be there for that. She won't - she won't need me."

Jim scoffed, withdrawing a few bills from his wallet with trembling hands and placing them beneath his empty coffee cup on the table. "Rick, you're the only family she has left."

The Becketts had a horrible habit of leaving him with gut-wrenching last words. Jim Beckett was found dead in the apartment Rick grew up in only a few weeks later, the alcohol bleeding through every pore of his body.

"You knew about it?" Castle asks, surprised by the news. He expected confusion and questions, was prepared to explain the last conversation he had with her father five years ago.

"He told me," she confirms with a small nod. "Near the end. I just… I never thought you'd show."

"I keep my promises," Rick shrugs, attempting to avert his gaze, to look at anything but her.

"You're a good man," Kate sighs, reaching forward, dusting her fingers along the collar of his dress shirt. The innocent touch nearly causes him to jerk. "I'm sorry, for what I did to you."

Castle immediately shakes his head in denial of her apology. "Johanna had just… I understood, Kate."

"That doesn't excuse it," she argues, the slender bones of her fingers clenching in the fabric, wrinkling it. "It's been five years and I should have - you deserved better. My best friend deserved better."

"I still hold such a privileged title?" he inquires, wiggling his eyebrows to make her laugh, the sound just as beautiful as he remembered, even when it's quiet and unsure. He breathes out the declaration before he can think better of it. "I missed you, Kate."

Her eyes are growing misty again. It's an emotional day, he reasons, her wedding and all. But the tears building in her gaze don't look as if they've been caused by the overwhelming joy or excitement most brides carry. Kate's eyes are filling with... something that looks like regret.

And then her arms are sliding around his neck, her scent embracing him with the cove of her body. His lungs fall useless, his limbs paralyzed.

Never would he have fathomed having Kate Beckett in his arms again.

Too much, it's just too much-

Where does he even put his hands?

"I missed you too," she whispers, the soft skin of her cheek brushing his. "I missed you so much, Rick. Every time I would see your books or stand in line at one of your signings-"

"You came to my signings?" he echoes, familiar remorse drenching his insides and his hands automatically reaching for her waist. "No, no, I would have recognized you the second you-"

"I always chickened out, stepped out of the line before I could reach you," she confesses on a sigh, the tips of her fingers finding the base of his skull, combing through the fine hairs there. She used to do the same thing when they were younger, always toying with his hair. Driving him crazy with it. "I'm proud of you though, proud of everything you've accomplished."

"Kate-"

"I kept track of the dedications."

Oh no.

"Pretty pathetic, huh?" he tries to joke, but Kate pulls back from him with reproach in her gaze.

"No," she answers. "They were… everything. Your books have been a lifeline for me, Rick. Ever since my mom - your books helped me keep my head above water."

"I could have helped," he mumbles, sounding like a child, jealous of his own novels. But they were allowed time with her when he wasn't, they were granted her acceptance while he was left to build a life without her. His best friend and the girl he fell in love with over the span of ten years, leaving him with a hollow, gaping space in his chest.

But apparently, she's fallen in love with someone else.

Castle reaches back, curls careful fingers around her wrists and draws her arms from around his neck, detaching her. How the hell is he supposed to give her away to another man after that?

"Castle-"

He swallows at the use of his acquired surname, can still remember narrowing it down with her help, how she started calling him Castle on random days just to make him grin.

"You're getting married in twenty minutes," he states, brushing his thumbs along the bones of her metacarpals despite himself, relishing the heat of her skin beneath his hands. "And maybe - I don't know if walking you down the aisle is necessarily the best idea anymore, Kate. I should just… I should go-"

"No, wait," she protests, her hands twisting, tangling with his. His eyes dart to her face, surprised by the simmer of longing rippling through her features. He's seen it before, when he actually believed there was hope for them, when he was so in love with his best friend that he couldn't fathom it any other way. When they were young and free and blissfully unaware of what the future held. Of dark alleys and bloodstains, of death and deconstruction and broken hearts. "I thought - I want you here, Rick."

"I can't be here," he scrapes out, clearing his throat and gracelessly withdrawing his hands from the delicate embrace of her fingers. "Can't be your best friend," he repeats those last words from her, but the anguish that bleeds in her eyes is enough to make him regret it. This is bad, going all wrong so fast, too fast, and he needs to go. "It's been five years and I - I don't even know why I came here, why I thought I could do this when I'm still so…"

The expression of heartache softens, a strange mixture of knowledge and curiosity, even an odd flicker of hope, flaring to life in her gaze.

"Still so what?"

Fuck, it's been five years and she's undoing him in five minutes.

Castle drifts forward, presses a kiss that exudes far too much sorrow to her forehead. One last goodbye. He needs to tell her goodbye.

"In love with you," he murmurs, unable to stop the plea, the contradiction, from spilling into his voice. He already hates himself for doing this to her, for ruining her wedding day with his own selfish wants. For still wanting her.

He's spent the last week preparing for this day, insisting to himself that his feelings for her were finally put to rest, that they were never anything but silly childhood nonsense to begin with. But just the sight of her after so long without her has spilled gasoline all over his heart, set it aflame for the first time in years. And he can't do it, can't watch her marry someone else. Can't be a part of it.

"So don't say yes," he adds, the forbidden words scraping past his throat, eliciting a hitch in hers. "Not if you don't love him, Kate. Don't say yes if he doesn't love you like I could."