How is Dimmesdale's internal conflict self destructive?

The Reverend Arthur Dimmesdale’s internal conflict in The Scarlet Letter stems from his external hypocrisy. He has engaged in a passionate romantic and sexual affair with Hester, conceived a child with her, and then allowed her to suffer alone at the hands of the community.
As a minister, Dimmesdale is supposed to be a paragon of the virtues he espouses from the pulpit. Dimmesdale is just a man who gave into temptation, but he can’t reveal this weakness without sacrificing his reputation and career. Knowing this, Hester refuses to name him as the father of her unborn child, wanting to protect someone she respects.
As time wears on, Pearl grows older, and Hester continues to don the scarlet “A,” Dimmesdale becomes overwhelmed with guilt. He punished himself physically and mentally in order to atone for his sins. Chillingsworth describes Dimmesdale’s turmoil thusly:

". . . he fancied himself given over to a fiend, to be tortured with frightful dreams, and desperate thoughts, the sting of remorse, and despair of pardon; as a foretaste of what awaits him beyond the grave."

This summarizes Dimmesdale’s infernal conflict perfectly because this shows that his greatest fear was that he would be condemned to hell not only for committing the initial sin but also for concealing it. His health continues to deteriorate until he grows pale and frail.
In the end, it is this internal guilt that causes Dimmesdale to die upon the platform as Hester and Pearl stand beside him. When he reveals the undescribed mark on his own chest, the reader infers that he bears a version of the scarlet letter on his chest. Finally exposed, Dimmesdale allows himself to collapse and die knowing that he may have redeemed himself enough to earn God’s grace.