After the battle of New York and everyone moved into the tower; they all assumed Clint and Natasha were a couple, but the fact is; they used to be...
When Natasha had first come to work for SHIELD she'd been partnered with Clint; Fury had warned him it was his responsibility to keep an eye on her. Their partnership went from strength to strength and in less than a year they'd become SHIELDs top field agents.
They became a couple a few months later. It was slow and delicate, neither knowing where they were heading, but it soon evolved into a full blown relationship and it scared them both to admit how much they needed the other.
Then it all went downhill.
A mission in Marrakesh had gone drastically wrong; Clint had overstepped his mission parameters in order to protect Natasha; he took a bullet for her and was knocked unconscious. Enemy agents were alerted to their presence when the alarms sounded; the building was set alight, explosions rocked the foundations and Natasha's instructions came through to leave all casualties behind and get out with the data drive she'd stolen, at whatever cost.
Natasha ripped the com unit from her ear and shoved it in her pocket; there was no way she was leaving Clint. She managed to get him down three flights of stairs and take out seven guards before the roof came down on top of her.
They were trapped, the coms had lost their signal, and as far as she was aware no one was coming for them. Clint had woken, but he was still losing a lot of blood from the bullet wound through his shoulder. They'd been trapped for well over 10 hours by now. He grasped Natasha's hand and was worried to find it cold; she was freezing, her leg was trapped beneath debris and she had a nasty head wound. She turned slowly to face him, forcing a smile to her face
"You should have left me Nat"
"Couldn't do that" she said, coughing as she inhaled, the movements caused a shooting pain up her side from her crushed leg and she winced
"Couldn't have left you either" he smiled at her
"You shouldn't have got in the way"
"He would have killed you Nat"
"Would have been better than us both dying" she said sadly, referring to the predicament they were now in
"No it wouldn't" Clint replied softly, squeezing Natasha's frozen hand gently in his "I love you Natasha"
"I love you too Clint" she whispered, before slipping from consciousness
"Tasha, Tasha?" Clint tries desperately to wake her, but nothing worked. Tears slid down his face and he too slipped into unconsciousness.