It was in Avengers: Age of Ultron that romance between Bruce Banner and Natasha Romanoff first blossomed but that's a plot point which wasn't touched on in Avengers: Infinity War aside from a glance the two heroes shared. Scenes in the trailer pointed to them having a conversation about things at some point but that wasn't included in the final cut so their relationship status is now up in the air.
During a recent Q&A, Joe and Anthony Russo were asked about why this romance has become part of the Marvel Cinematic Universe when it was never in the comic books to which he explained, "That was a Joss Whedon decision so it's not something I can speak to." He did, however, elaborate on the thought process the filmmaker might have had when he attempted to pair them up back in 2015.
"We don't directly translate the comics to the films -- why go see the films when you know how it's going to end?" Russo (diplomatically) said. "And it isn't a translation. It's our interpretation for the MCU. I think Joss was trying to find interesting ways of pairing up the characters and create dynamics between them. I know it seems a generally unpopular choice. You know, you can't win them all."
Finally, Russo addressed where things now stand between The Hulk and Black Widow and it sounds like things between them are definitely over. "Look, he disappeared for two years," he added. "She's pretty self-sufficient, she didn't wait around for him. There's sort of unspoken truth that there's need to be a spoken resolution." Are you guys disappointed that things between the heroes are over?