Why does Mr.Dimmesdale feel regret?

Dimmesdale regrets not taking responsibility for his own actions. He has allowed Hester to experience the public shame and punishment alone, while he continues preaching. As the story progresses, Dimmesdale actually inflicts more punishment and torment upon himself than Hester received from the community. The more his guilt weighed upon his heart, the more vociferous he became at the pulpit. When he tried to admit his own guilt, his congregants couldn't see it and held him up even higher as an example of goodness. Dimmesdale couldn't live with it and began to abuse himself...... he regretted his own lack of courage and regretted turning his back on both Hester and Pearl.