Early on in the episode, Kurt, Blaine, Brittany and Santana have their queer community. Later, there are allies, too, as Burt works with Hiram and Leroy Berry. Burt must have come a long way in his thinking since Kurt was three. He had time between when Kurt was three and when he was sixteen to consider a good deal about what having a gay son was like, and from sixteen to eighteen to deal with more of it directly with Kurt. Burt seemed to have a good comfort level with Hiram and Leroy.
Finally, Kurt and Dave find a sense of community and friendship, too. Kurt had always had that bare sense of community as far as believing it unethical to out Dave, even when threatened. It became much more than that after "Born This Way," until finally Dave became a real part of Kurt's community.
It was interesting how Mercedes related the story of Dave being outed. It was simply that he was seen with Kurt. That was enough to do it. Kurt must have been aware of that being the reason. Joe Hart invited Kurt to come to the God Squad meeting, so Joe's comfort level with gay people has had to go up fast.
Things at William McKinley High School had evolved enough that Kurt and Blaine were holding hands in the hallway. That was the Saturday of Regionals, I think, and the only other person in the hall with them was Quinn. Still, it's huge progress from where it was for Kurt.
It was quite the spectrum of the queer community and allies. The other New Directions members are allies, and so are the Warblers. Blaine wasn't alone back when he was a Warbler, and Kurt had people giving him support. There were six gay male characters on the show, when sometimes before Kurt had felt like he was the only one. Times have changed.