Some (most?) interpretations of the Gospel accounts have Peter despondent after the Resurrection of Christ. The account of John 21 is often taken this way. Verse 17 certainly seems to indicate that Peter’s grief over denying Christ three times persisted.
Right now, I can relate. No, I did not deny Christ three times during the Triduum. But in the midst of it, right before the Easter Vigil, I had a very sudden and very unexpected falling out with a friend. He did not even talk to me or let me know he was unhappy about a matter. I got the news second hand.
With 20-20 hindsight, I would have done something differently, yes. But I cannot reasonably take the blame for the falling out. How can I when I was clueless there was a problem in the first place? Nonetheless, I’ve been moody and fatigued since. I’ve still experienced the joy of the Resurrection. But it has been fleeting.
Easter reminds us that Christ and His people are victorious in the end. But we remain human. Dealing with disappointments, wrongs, and hurts from ourselves and from others can still drag us down, Great Fifty Days or not. Peter experienced that. And to a lesser extent I now am, too.