She may be perceived as a little OOC, but that's what exhaustion does to you, I guess, so I'm taking artistic liberties :) Enjoy!
She'd always thought herself well above such a base emotion as loneliness. As it was, it took her months to realise that the uneasy, greasy feeling coiling in her gut wasn't, as she'd initially supposed, weariness from the mission in New Zealand, or the subsequent missions stretching her abilities tight across the world.
No, it hit her as she lay shivering on her bed, silent sobs wracking her body as she woke from a particularly violent nightmare and reached, unthinkingly, blindly, for the body that was no longer there.
As her hands grasped the roughspun woollen sheets instead of soft, worn cotton, and her eyes fell on cold wall instead of a warm, smiling, concerned face, the realisation that she was alone, truly alone, smacked her in the chest; she was left reeling, gasping desperately for air as more sobs threatened to choke her, as the cold of the Serbian winter froze the half-fallen tears to her cheeks and her heart, so carefully hidden and protected, seemed ready to shatter against her chest.
The next morning, as she regarded herself dispassionately in the cracked mirror standing sentinel over an equally cracked sink, in a dismal bathroom with cracks gracing every surface, even herself, it seemed. The cracks in the mirror's surface split her face into discordant shards, and she couldn't help but marvel at the irony.
After that morning, the heaviness settled within her, wearing her down slowly and surely, making her more ruthless, more cunning, more desperate for something to make her feel again. She took more risks and more lives, remorse as foreign a concept to her as humility was to Tony. She lost count of the scars she gained spent fighting the loneliness that ate away at her, until finally, finally, the exhaustion won and the team refused to let her leave, even if she had wanted to.
She hadn't wanted to.
She's lying in her bed in Headquarters, curled as small as she can to conserve heat as the shivers race through her small frame, juddering the bed frame in their severity. She doesn't know when she last ate, she just wants to sleep but her traitorous mind won't let her. She hears whispers outside the door, footsteps and curses and what she thinks is a fist slamming into the wall. The shivers stop.
The door pushes open and three people step inside. Steve, she guesses, and Rhodey, and…
"Bruce?"
Her voice sounds dead even to her own ears, dry and cracking. She pushes herself up, back still to them, trying to still her suddenly rapidly beating heart. It must be, she thinks.
"Nat, I…"
She can picture him, clear as day, hands held out, palms up so he's not a threat, a grey cardigan slouched across his shoulders. Grey slacks and a white shirt, maybe, comfy but practical.
"You left… Why?"
The others leave them to it, and they talk. For hours he sits on her bed and strokes her hair as he tells her of the amazing things he saw and did, the people he helped and how every moment of every day his thoughts were tinged with sadness for missing her, and regret for leaving the way he did.
At last, they fall silent as the shadows through her window lengthen and turn inky. He curls on his side with her curled into his arms and kisses the top of her head.
"I missed you," she whispers as she finally relaxes into sleep.
"I know."