AN: Thanks to Justicerocks for the writing prompt! I love, love, love these two together, and it's so much fun writing them. Enjoy, and I welcome any others! xx

Perfect Fit

...

"There you go little man," Will says as he tightens the brunette boy's jacket. He gives a quick smile as the boy giggles with happiness. "As a doctor, I have to make sure you stay extra warm out here during the cold Chicago winters," he finishes, poking the little boy gently in the chest, his finger brushing against one of the buttons of the boy's winter coat. The little boy giggles once more, which in turn, causes Will to smile a bit bigger this time.

It's as if Owen Manning were indeed his own son, and he likes the feel of it, very much. A warm feeling creeps into his heart. Will gives Owen a light push on the swing and observes how happy the boy looks as a light snow falls, covering his hood with white flecks. He thinks this is a moment he'll never forget.

As Owen comes back down, Will grabs his small boots and tugs at them slowly, bringing the boy closer to his chest. He buries his face in Owen's jacketed body, before picking him up from the swing and holding him in his arms. He lightly kisses Owen's head before whispering in his ear, "ready to go see mama?"

Owen simply points to where Natalie is sitting on the park bench only a few feet away. She waves at her son and smiles at Will. He will never stop loving her smile.

"What're you two boys up to?" Natalie asks as they near her. She reaches out and takes Owen from Will's arms, cradling her son like any mother would do.

"Just swinging," Will replies, stepping behind Natalie so he can see Owen's face once again.

His cheeks are rosy, and it's the first time Will realizes how much Owen looks like his mom. It makes him grow even warmer inside. He rests one hand on the small of Natalie's back while the other reaches to grasp the little one's hand. Owen giggles. That's all he seems to do when Will's around, apparently.

"You make him laugh," Natalie chuckles, throwing a glance over her shoulder, her gaze meeting Will's.

"What can I say? It's the Halstead charm," he teases. She notices his smirk right away and rolls her eyes playfully.

"You're lucky that it works on 18 month year olds."

"What? It didn't work on you?" he questions, moving to wrap his arms around her waist and kissing her neck softly. He hears a light and content sigh escape Natalie's lips. She turns around to face him, still cradling Owen in her arms. The three of them make up the perfect family picture . . . a perfect fit.

"I never said that."

Will, satisfied for the moment, takes Owen from her arms and wraps him in a warm hug.

"Ready to go, bud?" he asks, tapping the boy's nose. He squirms in Will's embrace and bobs his head up and down, playfully poking Will in the chest.

"Dada . . . "

Will is caught off guard by Owen's words and darts his eyes quickly to Natalie's to examine her reaction. He sees her face slowly growing pale, and she refuses to make eye contact with him. The dynamic between the two suddenly shifts, and she reaches for her son's small body.

"We actually have to go run some errands," she mumbles to the ground, still refusing to meet Will's gaze. Finally, she looks up and takes in a breath, "but thanks for playing with him."

She can see the hurt cross his face, as his forehead creases, and he brushes a gloved hand through his hair.

Why is she reacting this way? he thinks

He didn't even do anything, she tells herself.

"Alright. I'll call you later."

Will settles himself in front of the television, beer in hand and Chinese take-out on the table. As he brings the bottle to his lips for another sip, he hears a knock at his apartment door. He glances at his phone thinking he may have missed a text from one of his coworkers saying they'd be coming over, but he sees nothing.

Getting up slowly and turning down the volume on the TV, he looks through the peephole and sees Natalie. She tightens the scarf around her neck and shifts impatiently. He smiles and opens the door, leaning one arm on the doorframe.

"Wasn't expecting to see you so soon."

"I owe you an explanation," she responds, "about today. I may have overreacted."

Will raises his eyebrows and crosses his arms over his chest.

"Okay, fine, I did overreact," she corrects.

"I know," he adds quietly.

"But I had a good reason for it."

Natalie moves closer to him, and he can practically hear her heart speed up. He swears his heart does too.

"It caught me off guard," she continues, "I didn't realize Owen thought of you that way."

"I didn't either," he pauses for a brief second and searches for her eyes, "but I'm okay with it." He takes a breath and continues to stand opposite of her, realizing the distance between them is only growing less visible.

"That's the thing, Will, until today, I didn't realize just how big a role you play in his life. You treat him like he's your son, even though he's not, and I feel so conflicted because I know he needs a father and it hurts me knowing he won't ever meet his real one . . ."

Natalie tries to contain herself but she feels the wetness of the tears begin to roll down her cheeks. She brushes a hand through her hair and looks down at her shoes, not wanting to see his face.

"Nat," Will whispers, moving to close the space between them and wrap her in his arms. She welcomes his embrace, breathing out shakily.

"I miss him so much, Will. It hurts. And just when I thought I had moved on, Owen came along, and he reminds me every day of the man I fell in love with. And it kills me knowing my son doesn't realize his father isn't here anymore."

He lets her cry into his chest, and all he does is rub her back and murmur quietly to her.

She looks up at him after a few minutes, and even though she had been crying, Will still swears she's the most beautiful woman he's ever laid eyes on.

"I want him to grow up with one though," she says quietly, smiling softly. "And maybe that's what he was trying to tell me, us, today."

"Us?" Will questions.

"You know what I mean." Her response is simple, and there's a sparkle in her eye.

"Do I?" he teases, bringing his lips down to capture hers.

He did, and it's a kiss he'll never forget . . . the kiss that sealed the deal and made him Owen Manning's father.