Dean didn't want to talk about Sam. He never wanted to "talk about Sam". Not now, not ever, and especially not with things the way they were. Like a band-aid placed pathetically over a huge and open gash. Whatever issues Sam and he had? Whatever problems? They weren't fixed. They were buried. Because Sam didn't want to push and Dean didn't want to deal, was too tired to deal with. He hated being suspicious of his brother every five seconds. He hated not trusting Sam. He hated doubting him the way he had been since he came from hell. So after Lorne's reading of Ruby? Dean just ... stopped. Except he really hadn't. It was still there. In the fact of his mind. The doubts. The worries. Even some of the fears, that despite Ruby's big confessional by his hospital bed a few months ago, there was still something they weren't telling him. Still something that could rip them apart. Yeah, rip him and Sam a part. Before hell, Dean never would have imagined it possible. Now ...
He didn't want to talk about it. Which was why he avoided. He was defensive. He didn't look at Cas when he asked, the question. "What about Sam?"