TBH, that is a thing that happens with a lot of other pairings as well. I mean, there's an awful lot of unexplained Tony/Steve or Natasha/Bruce or Natasha/Maria that pops up in the background, just for an example (I'd say "unexplained Tony/Bruce" but really, the movie did build that one pretty well). There's at least some interaction between most of those characters, but even so, it's abrupt to suddenly have a romance plopped down like of course it exists.

I've gotten to the point where I just roll with it unless the ship actively squicks me. Avengers is a crazy fandom.