Natasha had met Clint before he had children. He and Laura were not even married. As the story goes, Clint was sent to kill Natasha, but made a different call. That different call was saving her. He didn't just let her live, he also tried to save her morally. He brought her into S.H.I.E.L.D. with the hope that she could do some good; save people. Natasha was afraid when he brought her in. She thought that thinking she was safe may open her up for greater dangers. Forget being killed, now there may be torture.
At first she was to stay on her own in a dorm of sorts at main base, but she couldn't do it. Natasha had nightmares every night, and began begging for death like she did when Clint encountered her. After about a week, someone high up – Fury, Natasha later found out – made the call to send her to live with Clint.
This scared Natasha even more. She had been trained around women. She had only encountered men on her missions and they were not good men. Sure, Clint seemed decent, but the worst of men usually seemed decent at first.
Natasha had lived with Clint for two months before beginning to trust him. He had introduced her to new things – mainly foods. He also trained her, always offering breaks, which Natasha never took.
After six months, Natasha had grown fond of Clint. She had never experienced love, she did not know that's what was developing so she never tried to stop it. At the time, Nat didn't know, but Clint was becoming very fond of her as well. Their hang outs began to lengthen and conversations became more personal rather than about how the new Thai food restaurant was, but about ambitions.
Around month nine, Natasha was being sent on missions. Clint was with her every time. Some were group missions, but others were just the two of them. On these missions, Natasha was usually the one face to face with the target, and Clint was the eyes from a distance.
But one time the situation was a little different. Fury had called Natasha and Clint into his office. This was just like every other mission: get the details, prepare, complete, debrief. For this mission though, Barton was to be up close with the target, as well as Natasha; they were to be undercover as newlyweds.
Natasha remembers leaving Fury's office queasy. When they met at the local airport for the start of the mission, Clint was in perfect character. Natasha had difficulty adopting the new loving wife persona. Half way through the mission, their characters were invited to a formal event. The event required Natasha to be in a floor length, bright red dress with her hair hanging in loose curls and matching lipstick, while Clint donned a sharp suit. Usually on the big screen, the girl appears and the man is frozen and speechless because of how beautiful she looks, but in scenario, it was Nat that was in shock. For a man that wore either sweat pants or nothing ninety percent of the time, she did not expect him to look so handsome. When they reached the event, the two socialized with their target and the other guests. Near the end of the night, the target's wife had finally convinced the target to dance. To keep a close watch on the two, the agents followed them onto the floor. The music was slow, but neither stepped on the other's toes. Half way through the dance, Clint made a joke that made Natasha giggle for maybe the first time in her life. The two continued to sway and turn and Nat laid her head on Clint's chest. She could barely hear his heart over the music, but she could feel it somehow; not on her temple, but in the soles of her feet and in her fingers. Clint whispered her name causing her to look up. A split second of eye contact and then Clint leaned in. The two had stopped swaying; they were kissing. It was a real kiss. Not one for a cover with a target, but between two people that ached for each other. Natasha's hands slid over Clint's chest, while Clint's shot into her hair. Electricity flowed between the two like a lightning storm in the middle of the dance floor, though none of the other guests seem to notice.
After that night, Natasha and Clint were more than just teammates. Lovers didn't sound right to Natasha, and friends left out everything they were to each other. They wound up settling for partners.
Their partnership lasted two years. Natasha had opened up, and Clint settled down. Natasha told Clint almost everything about the Red Room, and Clint explained almost everything about his childhood. One night while watching a movie in their apartment together, Clint mentioned how one day he would like to start a family. Natasha knew he had said 'would like' but could tell how much thought he had actually put into this. He explained how they could have little gingers running around on a big farm. They could retire from being assassins and get a dog. Thankfully Nat was laying in front of Clint so he couldn't see the tears slowly crawling down her cheeks. In the Red Room, they removed any chance of Natasha ever starting a family. But, that was years earlier. The next day, Nat hopped in a cab and went to the doctor's office. There they told her there was nothing they could do. The following afternoon, she went to the lab in S.H.I.E.L.D. where there they told her the same terrible news. Silently crying in the cab ride home, Natasha had come to the only conclusion she could think off: ending things with the only person she had ever felt something for.
That night when the Widow reached her and Clint's apartment, Clint had dinner already prepared. The conversation was severely lacking, partly because Nat was determined to end whatever her and Clint had no matter how much it would hurt her, and partly because Clint seemed on edge. At the end of the meal, the worst thing that could have happened, did. Clint pulled out a rectangular box. Inside was a silver, arrow necklace. He explained that in their profession, having a ring would be a bad idea – "You couldn't wear it on missions because you usually have to flirt with the target and you can't do that if you're married," he laughed nervously – and how he's had the necklace for a month, but was waiting for the perfect moment to ask: "Will you marry me?"
Natasha was shocked. She couldn't say yes, so she said no. When the word was released from her lips and hit Clint's ears, she wished she could change everything that had happened and that would happen because the 'no' had broke Clint. She tried to explain a lie, something about cheating or never loving him. Natasha never remembered the lie that she told, but the image of Clint broken never left her mind, it was branded onto her eye lids.
After that night, Clint and Natasha didn't see each other again for six months. When they did it was formal. They began to work together again for S.H.I.E.L.D. instead of the individual assignments they had been on. When things went back to normal, Clint gave Natasha the necklace. She tried to decline, but he wouldn't take no for an answer, which was secretly fine with her because she had really wanted it.
A little while later, Natasha had found out that Clint had been seeing a waitress, Laura, when he had her gotten pregnant. Clint had proposed, knowing that things could be worse. Laura loved him and he had strong feelings for her, and he was finally getting the family he always wanted. Natasha attended the wedding. She was glad for she thought that her best friend had gotten the life he had wanted: a woman he loved and kids.
Natasha became an aunt to the mini Bartons. Laura was nice and always pleasant to Nat. Natasha did not know that Clint had never told Laura about their relationship, but Laura suspected. When Nat began having a relationship with Bruce Banner years down the road, Laura was happy thinking Nat may have finally moved on. But Nat didn't.
Natasha Romanoff desperately tried to be in love with Bruce. She had seen enough romance movies with Clint in the years before. She tried to be the damsel in distress, but in the end Bruce – or the Hulk – decided she wasn't worth it. Later when speaking with Fury, he told her how he hoped she would find something there with Bruce, though many years ago he had hoped the same for two other agents and that didn't work out.
Judging the outcome and looking back, Natasha wasn't sure if she had made the right decision. At the time she thought Clint was happy, but he was away from home so much and spends all of his time at home trying to fix rooms that seem fine.
Maybe she if she would've told Clint about her condition he would've stayed. But twelve years later is probably the definition of too late.