Well this would be interesting. Luna’s father SlenderMan wanted to meet Ayano. And she was fine with that but…thing was that the rest of the CreepyPasta family was unaware of her ‘relationship’ status.
Some people would have pushed the matter further, insisting. But Sam knows his brother, and he respects him. So when Dean says ‘Don’t’ Sam nods and keeps listening. Of course he doesn’t think it’s Dean’s fault. But he knows that this isn’t the right time to talk about this with Dean.