I feel that neither armaan was wrong in asking jassi abt that nite, becos if anyone was in his place, would have done that, we cant expect extraordinary things from a human. Only thing that was wrong was, he must have made clear what he saw.
Coming to jassi, she thinks armaan doubts her only becos she stayed with cj in one room. she does'nt know what he actually saw. But i feel jassi must have stayed and made clear that she soesnot want to marry armaan, instead of leaving like coward.