https://www.businessinsider.com/hbos-the-last-of-us-episode-three-review-bombed-homophobic-2023-1
Neil Druckmann, the co-creator of the series who also developed the video game, told The Hollywood Reporter that Bill and Frank's relationship "went over a lot of people's heads" in the game.
"At the time, [the subtlety is] what helped get it in," he said. "It's sad to say, but it would have been controversial otherwise."
I'm amazed it would go over anyone's head in game. I know you could miss a letter from his boyfriend or something if you were careless, but it wasn't like Bill being gay was only being hinted at.
There's literally a cutscene in the game where the characters stumble upon gay porn mags left in a car from Bill lol. Nothing subtle about it
Perhaps he's just a dude who likes the aesthetics of gay porn