That took the wind out of Sam, like a punch to the gut. It didn't hurt, but it left him a little bit speechless. He was used to being the one that was constantly fucking up. That was always ashamed of what he'd done. That was, well, under the influence of demonic power.
He didn't know if he believed it, not entirely. At least, he wasn't sure that had been the real reason why Dean had made the choice to cure himself alone. Truthfully, it was hard to know what to believe anymore. But he sympathized with the sentiment.
He looked down at his hands. "Yeah, I know the feeling," he said wryly. He had fucked up so many times already, and would do it again multiple times in the future. He wasn't going to make anything any better between them if he made Dean feel worse, even if he didn't feel better about the whole thing, and it was pretty obvious that he wasn't going to change Dean's mind. He took a deep breath, and forced himself to put aside the rest of his upset-- for now. "Don't worry, I'm sure you've still got a few more mistakes to go before you catch up to me."
It wasn't quite letting Dean off the hook, not quite forgiveness, but it wasn't accusing him anymore, either. It was acknowledgment that he knew what fucking up was like and that sometimes stupid decisions were made to avoid it. Which, in turn, were mistakes. But if he hadn't driven that point home yet, he didn't know if he would. It was infuriating, but he was getting nowhere with that argument. His jaw tightened, and then relaxed a little bit, but there was still a determined hardness to his expression.
"So," he said finally. "The soulsword doesn't work. We'll find something else. Something better."