In Avengers: Age of Ultron, we saw a spark between Black Widow and Bruce Banner. Will we see that relationship finally become something more in the upcoming Infinity War? With so many things going on one wonders if a movie with so many characters will find time for these two to deal with their feelings. Our own Sean O'Connell asked Mark Ruffalo about his character's on-screen relationship when he visited the set of Avengers: Infinity War, and while Ruffalo was successfully vague in his answer, it does appear that these characters will be dealing with their feelings for each other for some time to come including in the upcoming film. Although, he also indicates things likely won't work out for them, regardless of whether or not they actually get together. According to Ruffalo...
They're star-crossed lovers, so it'll be something they're dealing with for the rest of their living days, I think. Whether it's requited or unrequited, I don't imagine that's gonna go away anytime soon, in one iteration or another.
Referring to the relationship between Black Widow and Bruce Banner as "star-crossed" is not a good sign, as that implies the relationship between the two is fated to fail. It's a somewhat understandable perspective. One of them is a trained assassin and the other turns into a big green monster every time his emotions get the better of him. Seeing such a relationship work out would be a long shot at best. However, Mark Ruffalo does imply that this is something the pair will be "dealing with" for a long time, so you can expect the item to at least be brought up during the events of Avengers: Infinity War. The first trailer did include a couple shots that implied the pair would share a longing look at each other, depending on the situation, there might not be time for much more than that.
Of course, Mark Ruffalo does also imply that the feelings could end up being "requited" at some point, which would indicate that the characters might be able to spend some time together, even if the relationship is ultimately doomed. That might be nice. The pair clearly has a lot of baggage to deal with, finding joy in each other for a little while would be a nice thing to have happen, they deserve to happy, right?
With Avengers: Infinity War barely over a month away a lot of storylines will likely be coming to a head. We don't really know what's in store for most of these characters, and the question of which ones will survive is still very much up in the air. If we lose one of these characters, then we can be fairly certain it will have a significant impact on the other as the MCU continues. We'll find out April 27.