FOUND - Dean/Sam vs. Azazel, on ao3
I read this several years ago on ao3. Started with John, Dean, Sam driving to Bobby's, I think. Sam was 16 or 17? Sam gets kidnapped by demons or humans who work with demons, and he gets tortured (maybe shocked, water was involved,...). Dean and Sam are intimate, Bobby is gay or at least bi. Some guy (Rufus?) gives Sam and Dean knives that they bind to each other. They spend awhile hiding at a hotel cause the owner was tortured by...something evil, so she has lotsa protections up to keep demons 'n things out. When they face Azazel, he reveals their intimacy to John, who loses it, and Azazel tries to like control Sam, but Sam has been cleansed of the demon blood through his relationship with Dean, so Azazel dies and John works to understand Sam and Dean's relationship.
That's about how far I read, I think, and I really want to read it again. If more detail would be helpful, I can definitely go into more detail. I feel like the name is on the tip of my tongue but I can't remember it.