I think it has to do with Sam. When the way Uriel said about how he knows just exactly which pressure to press,(or something in those lines.lol) was way too nasty. Like he knows something. I mean, yes, sure Dean would have to give up pretty much anyone for Sam but still..I don't know how to express, but it's like Uriel was saying "it did before."

I agree with some people above, about how Alister convinced Dean that Sam would never save him and that he would move on, etc..I think it was more on the line how Dean is foerever lost and alone, rather than "I would harm Sam if you don't give in.". Because latter meant Dean didn't have a choice but to give in without his intention, but the prior meant Dean did really breakdown, really give in.

I do think there had to be a non-con between him and Alister though. The way Alister treated Dean when he first saw him was way too sexual.