"Love you, Nat."
The first time Clint had said it was like nothing Natasha had ever experienced. They hadn't had a long acquaintance, but it had certainly been an eventful one. While trying to protect her from S.H.I.E.L.D. backup that had been recruited after he had refused his mission to kill her, they had gotten to know each other quickly, not out of curiosity but out of necessity. She had been surprised that they had meshed so well, both in combat and out. So, finally, when he seemed at his wit's end and it was looking like they might not have been able to elude their pursuers any longer, Clint had told her. After all, Clint had thought, why else did he want to save her? Why else would she make his heart drop with just a smile? If that wasn't love, he didn't know what was. So he told her.
In return, she stared. She was quite literally unable to respond; and she didn't, until many days later, when they had recovered and S.H.I.E.L.D. had decided to review Clint's argument to save Natasha. She awoke slowly in the recovery unit, and it was several seconds before she noticed Clint sitting by her she opened her eyes, he greeted her with a kind smile, and before she could recall the preceding events, she smiled back, wholehearted and unabashed. It was only when she began to recall those words-his words-that she withdrew, thanking him tersely for saving her and chatting casually about what they could expect from S.H.I.E.L.D. He did not bring it up again.
It was months later that their relationship had solidified; while Clint was perfectly content being around Natasha as her friend, she was startled when she began to develop feelings of affection for him. To say that she was shut off from her sentiment would be an understatement; she denied it to herself, again and again, coming up with reason after reason why she should never feel strongly for anyone. So, it ended up sounding much more like a question when she did finally manage the words.
Clint had been debriefed on a brand-new weaponry technology, and issued a prototype of the new weapon in development, created with him in mind. He was nothing short of ecstatic as he explained what he had learned to Natasha, how proud he was that they had modeled it for him; he held the length of an ordinary-looking arrow in his hands and rambled about the processes by which it could detonate with a 20-foot radius. Natasha was only half-listening, though. As he continued enthusiastically, she watched him: his genuine smile, his easy confidence in her, his laugh. And, quite similarly to Clint's admission to her, she blurted out, unplanned and awkward.
"Love you, Clint."
It was worth every expression that washed over Clint's face; disbelief, confusion, amusement, and joy, all in one smile. She couldn't hold hers back, either.
Her three words were what began an era of absolute devotedness from Clint; whether it be flowers, chocolates, frequent rib-crushing hugs or an over-the-top gift for an anniversary or holiday that had slipped Natasha's mind, Clint was nothing if not unrestricted in their relationship. Natasha was determined to open herself to that sort of foreign affection, and to reflect her feelings for Clint as unabashedly as he did. It proved much harder than it looked.