Dean knew that his father was right, that no matter what happened he'd still be the person there for Ben, the one that really wanted to be his Dad, and that would be great. However, he also knew full well the way he had looked up to his own Dad growing up (the way he still did if he was being honest), and he knew that there really was no substitute for a parent. He fully intended, if this didn't work out, to tell Ben that he could still call him 'Dad' if he wanted to, but something wouldn't be the same.
However, Dean had almost always accepted John's opinion, his orders, as nothing less than law, so when John told him that his fears weren't going to happen, that the test was gonna work out for them, Dean relaxed slightly. The tension was still somewhat there and probably would be until that damned piece of paper came back, but he trusted his father enough to feel a little better...about that anyhow. After all, he did really love Ben, even if neither of them had dared to say it yet.
Part of him knew that he was already latching onto the kid as hard as he could. He wasn't sure if it was the best thing for Ben, if his best was enough, but he knew he was damned sure gonna try. Ben deserved it. For a moment the knowledge that he was gonna try, and that his Dad thought this was gonna work out, was enough.
But there were other things, questions and emotions that were gnawing at him. He had wanted to talk about this with John for some time, not because either of them were good at talking, but because John was quite possibly the only person here who could possibly understand what was going on with him. More importantly, he was the only one who could give him any advice on how to deal with it.
"How long?" Dean finally asked, his voice ragged. He was unsure if he even wanted to know the answer, but he didn't WANT to know as much as he needed to know. Though there would be no right answer, there seemed a power in knowing, in hearing verbal admittance that he had not been the only one broken down in the pit. "how long did you last, Dad?"