He took a deep breath as he watched her. Really, this could be going way better if he hadn't just laid it on her like a big ole freak. But how was he supposed to dance around the subject when it was so hard to lie about something like 'He just popped up like a daisy'. There had to be consequences to that. And he was paying it with his own blood. There was some regret, yes. But protecting Sam was his job. Something John had hardwired into his head when he was a kid and he was keeping to what he was meant to do. Which was protect his brother and die for the cause.
Even though he didn't want to die like this. Not right now. Hell, he hadn't even made it to thirty yet and this was how he was going to go out. Not with a blaze...but a little flicker before getting dragged off into hell. Though he was brought out of that little mind trip as Jo's fist connected with his face, giving a small gasp before glaring over to the blonde woman. He knew why she did that. He didn't blame the girl either. He would have reacted the same way.
"He was dead, Jo. I fucked up and got him killed. It was my job to protect him and I got him killed." He still remembered watching the light in his baby brother's eyes go out as in that empty street. Holding Sam just as his heart gave out and Dean's life feel through. The older Winchester did something he hadn't done (in front of Jo, at the very least) for a while as he cleared his throat, wiping away the tears on his face. "It's my job..."
And this is how much John Winchester had fucked up his son's mind. Dean wanted to hide in the excuse that this was his job and that he was perfectly fine with it. But he wasn't. And he knew he wasn't. "I held him in my arms when he died, Jo. Do you have any idea what that feels like? Any idea..." His voice cracked a bit, filled with emotion for a moment. Regret, fear, anger...all building up inside him.
"I didn't know what to do." His voice was small, nearly in a whisper but it was the truth. He hadn't known what to do.