Dean made sure not to look at Cas as he flirted with the waitress, he smiled and flirted but not once did his eyes leave her face when years ago he's eyes would have automatically gone to her breasts which were pushed up and on display. She was a good looking girl, he could admit that to himself and years ago he would have been all over that but now he wasn't interested.
Cas clenched his jaw and looked away when Dean started flirting back with the girl. He knew that Dean wouldn't take it any further than flirting, in fact when he looked over at Dean (which was a lot more frequently then he would like to admit) he noticed that Dean's eyes never left her face and he couldn't help but feel please about that. Years ago Dean would have picked up the girl but now Cas knew he wouldn't.
The two of them were in limbo, not together but unable to be apart, a couple but without admitting (even to themselves) that they were. Everyone knew it, for Chuck's sake almost every single demon and angel they met made a comment on it, even Cain realised but no, neither of them had admitted to it, no matter how obvious it was to everyone else.
Dean knew that eventually one day something would happen and they would be forced to talk about it, for chuck's sake he had basically admitted it himself a handful of times but something always stopped him but he was never really sure what it was that did, just that somehow he knew it wasn't the time or he was scared, he wasn't sure which it was if he had to be honest.
Cas knew eventually something would happen they would admit to their feelings but it wasn't time, they weren't ready.
Both knew they had things to work on, Dean's abandonment issues and how he needed someone to stay without him asking, for someone to believe he was worth it and Cas's abandonment issues, how he needed someone to believe he was worth enough for them to ask him to say but they had a while to go. Both knew they had a few issues to work through before they would get together, before they could even admit to themselves what was going on but that was ok.
They played the game of Dean flirting with anything that would flirt back but at the end of the day he would be with Cas when they headed back to the bunker (or motel if they were on a case) and how Cas would get insanely jealous and stare off to the corner until it was time to leave.
They weren't ready for it yet but they were getting there.