From what we see and are told in the movie, apparently Luke didn’t even try to talk to Ben before going to him in his hut. And that’s just insane for me. We’re talking about the guy who surrendered himself to the Empire to have some alone time with Hitler to try to convince him that he’s actually a good guy.
Luke said that he had sensed some of this during their training, but had to be sure. It really doesn’t seem like the kind of thing that you ask someone about as a primary way of discovering the truth.