Quite a lot has taken place since Jesus told the disciples that they would disown Him. Quite a lot has taken place since Peter objected to that and Jesus told him he would deny Jesus three times that very night.
Jesus has been arrested, tried in a joke of a trial and been found guilty of blasphemy and condemned to die; Peter was outside listening to the proceedings. You might recall that when Jesus was arrested, Peter drew his sword and cut off the ear of one of the guards, but Jesus had stepped in to stop Peter, replacing the man’s ear. Then Jesus told the crowd off for not doing their foul deeds in public, and Peter, along with the other disciples had fled the scene.
The disciples had learned a great deal over the past few years from Jesus, but in spite of at least three warnings, they hadn’t quite gotten the point of Jesus’ mission as the Messiah; that He had come not to conquer the Romans and restore Israel as a Nation of the earth, but instead had come to conquer sin and death and establish a Kingdom not of this world. Jesus told the group about His real mission three times, each of which ended by Jesus telling them He was going die at the hands of the Jewish leaders, and then rise again from the grave on the third day. Yet in each instance, the disciples reacted to His death prediction and apparently didn’t notice the resurrection prediction.
Peter now knew that Jesus was about to die, but the resurrection part of the story still eluded him. Remembering Jesus’ words of earlier that evening, he now creeps of and weeps bitterly over his own rejection of his Master in front of those in and around the place of His trial. For Peter, relief from his agony was still far off, but he wasn’t the only one having a bad night; Judas, the betrayer was having a worse night.