I remember reading a fic and I remember Justin and Brian were talking and I think it was a post 5-13 fic where Justin says something along the lines of 'we communicate best when we're in bed' and I think they were talking about the gang not understanding their relationship.
Is there any fics while Justin and Brian talk while having sex? It's weird, I know, but I'm just wondering.
Thanks,
That Happy Feeling by Rizabeau was the first one I was looking for.
There are other fics suggested, links in comments.