I don't know if they've really outright denied him being bisexual, though. I mean, a lot of people involved with TWS have as good as said that the movie was a love story. If it was ever addressed in canon, I don't think it'd be a full on "I love you, now let's kiss" scene since "with you to the end of the line" is pretty much the closest you're going to get to two dudes saying they love each other in this type of movie.

And to be fair, the Cap movies are the ones least focused on het romance, so.