I agree and disagree.
I think the important thing to note is that he says, “We don’t need your help,” so I don’t see this as an inversion of the previous “I need you”s. The other two times were Dean saying he needs Cas, not whatever help Cas can provide. In Dean’s mind, these are very distinctly different things; he made the mistake of treating Cas like he was only good inasmuch as he was useful in the past, and after all the terrible shit that went down Dean makes sure (in his terribly poorly communicated way) not to suggest such a thing again. Because it’s not true anymore — they really don’t need Cas’s help. If they keep Cas around, it’s because he’s family, period. Dean just needs the stupid angel to be there, and he’s tried so hard this season to make Cas understand that.
But does Cas understand it? Well, clearly not. Dean may not intend for “We don’t need your help” to be the opposite of “I need you,” but Cas still interprets it that way. And that’s the real tragedy here. Dean’s thinking, “I’ve made this clear multiple times, and every time you just leave.” He feels betrayed because he’s bared his soul for Cas and gotten nothing in return; he thinks, for once, that he’s made his point clear. But Cas, for his part, hasn’t gotten the message. Perhaps on some level he understands what Dean has been getting at, but he certainly hasn’t accepted it. He still thinks he has to do things to earn his place in the Winchesters’ lives — that, oh, but if I can just do this good thing for Dean, everything will be okay again. Hence the comically/tragically desperate shopping incident.
Basically, if this scene doesn’t sum up Dean and Cas’s problems this season, nothing does. Dean thinks he’s being clear; he’s telling Cas the other half of what he’s been saying all season: “We don’t need your help, but I need you.” And Cas, bless him, still thinks that he can make things better by being useful, by going out and doing good things until Dean forgives him. The irony is that it’s quite literally the opposite; if he’d just stay for once and stop trying to take action to get back into Dean’s good graces, he would be back in Dean’s good graces. Goddammit.
Now, if you’ll excuse me, I’m going to go cry and punch a wall because these two are such oblivious morons.
Because a part of Cas still equates “I need you” with “You’re useful to me”. And he just doesn’t understand, not on any *reasonable* level, that he is something *more* to Dean than a nifty swiss army knife. He tells Dean, “Let me go with you (because I can be useful)” and Dean tries to tell him “Stay and get better” but all Castiel hears is (so you can heal and be useful later). He doesn’t hear the “stay” part at all.
And it just makes me what to rip my hair out.