He's sleeping.
After today she's hardly surprised. As soon as he rested his head against the top of the couch he was out like a light. He's told her he doesn't need as much sleep as normal people, but after everything that's gone down lately it's no wonder that he's spent. She's feeling it too – probably more so than he is. And yet she can't sleep.
Steve Rogers is a hell of a man. He perplexes Natasha; usually her co-workers are pretty much like herself; cold, calculated, mistrusting. He's certainly mistrusting, but he's so… Caring, so predictable – it's a chip in his armour, his compassion. Yet it's what makes him so him, and it's something that she's shocked to find beautiful. He's so innocent when he's sleeping. It's so unlike the cool frown he wears when awake, but his eyes always give him away. He may be a soldier, but he's not well-accustomed to the battle they're fighting right now. Hell, even she's not built for this.
SHIELD is her life, and it's crumbling right under her feet. She thought she knew her place in this world, but if worst comes to worst and they have to take this thing down then… What? What will she have? And what if she's carried out missions for HYDRA? She thought becoming an agent would help recompense for her past mistakes. And all of that will have been for nothing…
She inhales sharply, hating herself for being so emotional about it all. She's been through so much, why is this so difficult to deal with? Surely she'll get through it. She gets through everything. She glances back to the Captain, who's still sleeping peacefully; completely unaware of Nat's inner turmoil. She wishes that she could sleep, or that they were still fighting; anything to keep her mind off what's happening.
They seem to be the perfect partners-in-combat; Black Widow and Captain America. Even in the whole New York fiasco he was as well-attuned to her as she was him. They defended one another; he shielded her with such ease during a rather big explosion, he helped give her the lift she needed to get to STARK tower etc. And this mission has been no different. She could quite easily go as far as to say she'd be dead without him. An unusual surge of gratitude takes her by surprise, causing her breath to catch in her throat. She should really thank him for this. For everything.
He's such a good man. Everything Steve does is done to protect other people; for the greater good. He makes her want to be a better person. She wants him to consider her his equal, to put his trust in her. She wants him to be able to put his life in her hands as she has his and know that she won't fall through. She needs someone to believe in her; it's a vulnerability she despises, but if any man was meant to bring out her weaknesses she's glad it's one as kind-hearted as Steve Rogers.
She knows she won't sleep, but she heads off to Sam's guest bedroom anyway – she doesn't think she can stand being in the same room as him any longer. He's so good, so beautiful. If the guilt of her past crimes begins creeping up on her, with him around, she's not sure what she'll do. She can't trust her own emotions. Not around him.