Barney was so sure Cedric was going to win. SO sure. When he and Harry both took the cup he was a little disappointed, but at least Cedric did win, even if it was jointly with someone else. He assumed when the pair disappeared it was something planned by the tournament organisers - a last, hidden task - but when they came back he was just staring. He didn't cry he just... stared. I think he's in shock. At first he kept saying that Cedric was okay and Dumbledore was going to fix him and it would be okay but he sort of trailed off as that got increasingly obviously wrong.