She doesn't understand why he left.

All he knows is that he left because of her.

"Hey, Romanoff, you want to train? Sam and Rhodey are done…oh," Steve trails off when he steps into the living room and finds Natasha curled up on the couch.

"Nat?" he asks.

She glances up at him. He can see the tear streaks on her face. She swipes furiously at her eyes and meets his gaze.

"What?" she answers tersely.

He shakes his head. "Nothing."

She turns away from him, burying her head in her hands. He sits down next to her and puts his arm across her shoulders.

"Sorry," Natasha murmurs through her tears.

"It's nothing," he reassures her. "What's wrong, Nat?"

She's silent for a few moments. "Bruce," she whispers.

He's silent, too. Jealousy rises in him, but he quickly pushes it down.

She's suffering, Steve, he reminds himself.

"He…he'll be back," he says.

She nods and stands back up.

"Let's go train, Rogers," she declares.

He follows her to the training room. As they reach the entrance, she turns around to face him again.

"And Steve…thanks."

She feels guilty, but she's glad for the distraction. She's focused on Steve alone, as she calculates where to hit him next. He darts to her left, and she flips over him, landing behind him.

"Can't catch me, Rogers," she snickers, as she leaps onto his back and jabs him in the back of his neck with her fingers.

He winces and staggers back when she jumps off, landing lightly on her feet.

"Next time, Romanoff," he replies, sprinting towards her.

She nails him with a kick to his forehead, and he falls back.

"I win," she laughs.

"Yeah, yeah, whatever."

As they leave, she feels the familiar pain settling back in her.

She's thinking of Bruce again.

"I need you to turn this bird around," she tells Bruce.

On the screen, she can see the Hulk sitting in the cockpit.

She can tell that he knows exactly what he's doing when he turns the video feed off.

The screen goes black.

He's gone.

Natasha jolts awake from her dream.

What could she have done to stop him?

She knows there wasn't anything, but she still feels like it was her fault.

Steve stops in his tracks when he finds Natasha downstairs.

"You're awake too?" he says.

She freezes and turns around. He can see the flicker of disappointment in her eyes when she sees him and not Bruce. He knows that they used to meet like this, in the middle of the night. Especially after Wanda had brought back their worst memories.

"No, I'm sleepwalking," she deadpans, her mask back on again.

I'm the Black Widow. I won't let him see how I feel. This afternoon in the living room was bad enough, she tells herself.

"Dreaming of eating?" Steve teases when he notices the apple in her hand.

Second mistake. Nice going, Rogers, he berates himself, when he sees her wince.

"No, just dreaming of a close friend…leaving," she says nonchalantly, though her voice cracks when she says leaving.

"We'll find him, Nat. It's okay," he tells her.

"No it's not. Have you ever lost the one you love, Rogers? Have you ever lost anyone close to you? You don't understand!" she snaps.

It feels like she's physically punched him in the stomach. He closes his eyes as memories flash across his thoughts.

Peggy. Bucky. My family. Everyone I knew.

He looks back at her, and she can see the pain echoing in his sky blue eyes. She can see the mistake she's made.

The ice, she remembers.

"I was in the ice, Romanoff," he whispers. "I lost my family. I lost the one woman I've ever loved. I lost my best friend."

She's about to apologize, but he continues.

"I wake back up, and I find out that my family and Peggy are dead. I find out that Bucky is still somehow alive, but he's joined the enemy. I've lost everyone I've ever known."

"Steve…I'm sorry."

He shakes his head. "It's fine. You're in grief. I'll let you be alone now."

He turns and disappears in the elevator. She hears the doors slide shut, and the elevator begins to rise.

"Don't go," she whispers almost inaudibly.

He's already gone.

Days pass.

He still hasn't talked to her.

Finally, she decides to change it.

She can't lose him.

"Do you need something, Agent Romanoff?" he asks politely.

"Steve, please. Stop ignoring me," she says, standing in front of him. "I can't lose you, too."

He pulls her into a hug. "Sorry, Nat."

"I'm sorry too."

"It's okay, Nat. Really. I have good news for you."

"Yeah?"

"Dr. Banner is on his way back."

He arrives today.

Natasha doesn't know if she wants him to.

But regardless, he arrives.

"Natasha. I'm so sorry," he whispers when he greets her.

"I was so worried."

"Steve told me. I'm glad he helped you."

She nods.

"I love you, Nat."

For some reason, she tenses when he calls her Nat. It's a nickname for her closest friends to call her. It's only for Clint…and Steve.

She shrugs it off. What matters is that Bruce is there again. With her.

She doesn't notice Steve's pained look at them.

She doesn't notice when he disappears back upstairs.

He made her go through so much pain. She was suffering because of him. She doesn't deserve to be with him. Who helped her get through the pain? Me, Steve thinks.

Why does she still love him?

He doesn't know. But he knows that he wants her to be happy. So he won't say anything.

He won't try to end their relationship. He doesn't want to see her in pain again. He cares for her enough to do that.

But it's tearing him apart.