A/N: Prompt from Audrey: A huge, big, blowout fight. Say that Kate catches Castle kissing another woman? Obviously, he isn't cheating on her, but that's what she perceives it as.

"Castle?"

Her voice echoed with disappointment and hurt. He pulled away from the stifling and unwanted kiss to find his fiancee standing in the doorway, an expression of shock and anger decorating her features.

She looked stunning in the knee-length navy blue dress. It clung to her curves in just the right places, and the soft fabric swished around her knees. Her long hair was down, fastened out of her face by a sparkly silver clip. Her make-up was simple and elegant and her silver heels elevated her height by a couple of inches. She'd left work as soon as she could, in order to be here, at the launch party for Stunning Heat. He'd known she would be late, and for the first half-hour, he'd waited anxiously for her. Then, he'd gone to the bathroom, and when he emerged, he was practically assaulted by this woman-whose identity he had yet to discover-who had quite literally thrown herself at him only seconds before Kate had walked into the room.

Great timing, Universe.

"Kate," he began, taking a step toward her. "Please don't jump to conclusions."

"I can't believe you," she said. "I thought you weren't that man anymore, Rick. Clearly I was wrong." She turned on her heel and stalked down the hall. He didn't hesitate to follow her into a blessedly empty room.

"What do you want?" she fired at him.

"Kate, please," he pleaded. "Please, don't do this. Give me a chance to explain."

"Explain?" Kate repeated. "Explain? No, you left your right to explain back there in that woman's mouth! You don't get to make excuses and call it explaining!"

"Beckett, she threw herself at me. I didn't even have time to react before you showed up."

"Oh, come on," she scoffed. "She was your type."

"Kate, that's not fair!" he replied. "When's the last time any woman but you mattered to me?"

"Oh, let me think," she said scathingly. "How about…three minutes ago?" He groaned aloud.

"How many times do I have to tell you that I didn't do anything?" he asked.

"It doesn't matter how many times you say it, Castle," she snapped. "It won't change what I saw!"

"You mean what you think you saw," he corrected. "Because I know you didn't see me seduce that woman. And I know that because I didn't!" She shook her head.

"I can't listen to this," she said. "I thought I knew you. I thought we were 'Always'." She laughed mirthlessly. "Shows what an idiot I was, huh?"

"Kate, I thought we had worked past this," he sighed. "This…trust issue. I know a lot of people have hurt you in your life, but I have told you a million times, I won't hurt you."

"Well, you did!" she said. There were tears forming in her eyes and he wanted nothing more than to take her in his arms and hold her and make it okay. But he knew that he couldn't. She was likely to kill him right now if he did. That in itself broke his heart.

"What I saw back there? Yeah, Rick, that hurt."

"Kate, you know me," he said. "You do. You can't do this; you have to trust me, okay? Without that trust, we're going to fall apart."

"How am I supposed to trust you when I show up her-for you- and see that?" she asked.

"That's the point," he replied. "You have to trust that I had no part in that. You just have to trust me, Kate."

"I'm finding that a little hard right now," Kate choked, collapsing into a nearby chair. Castle crossed the room and knelt in front of her, hesitantly reaching for her hand. He took it as a tiny victory when she didn't pull away.

"Kate, please look at me," he pleaded. She raised her eyes to his and he held her gaze.

"I know you've been through hell in your life," he began quietly. "But I'm not going to hurt you, I promise. And I'm not going to leave you."

"That's what everyone said," Kate whispered.

"And that's where that trust comes in," he replied. "Kate, I love you. You have made me a better man. You brought me to a place where I can be me and not worry about what other people will think. I love you like I've never loved anyone before. You're my world, Kate, and nothing is going to change that, ever. I'm taken. I don't care who that other woman is, I'm not interested. I'm engaged to the love of my life, and I have no desire whatsoever to be with any woman but you. You just have to believe me on that, Kate." Tears were sliding slowly down her cheeks and he reached up to wipe them away gently.

"C'mere," he murmured, standing up and pulling her also to her feet. He wrapped his arms around her, holding her close."

"I'm so sorry, Rick," she said.

"Oh, Kate," he sighed, pressing a kiss to her head. "Shh, don't cry, honey. It's okay, Kate. It's okay." They held each other for a moment. Then, she pulled back and smiled slightly at him.

"Thank you," she whispered.

"For what?"

"Loving me. Being here. Being you."

"Always."