A/N: my headcanons have already been published at the Avengers Headcanons ( ). If you love this movie, go there! It's absolutely fantastic!
Disclaimer: I don't own the Avengers and the characters; I'm just borrowing them out of love and respect.
Budapest
Budapest is where Clint and Natasha fall in love with each other, but both keep it secret.
Natasha didn't want to ruin her relationship with the only partner she can work with. Clint, on the other hand, thought his feelings were unrequited, so he didn't show them. They worked and fought side by side for years and, despite their jobs, they never really believed they would not survive one of the missions, they both assumed they had time.
When Clint is mind-controlled by Loki, Natasha realizes they may not have time, that she had chickened out back there and she had wasted time hiding behind the whole I-don't-wanna-ruin-this-partnership-thing. Clint opinion is like hers, when he reverts to his normal self so, after Loki and Thor are back to Asgard he manages to gather all his courage and asks Natasha out for a coffee. Natasha tenses up, but she knows she will hate herself if she chickens out this time too (after all they had been through) and answers with a happy smile.
