In "The Scarlet Letter", why have Hester and Dimmesdale decided to return to the old world of Europe?
In the forest where she and Arthur Dimmesdale are unrestricted by society, Hester convinces her lover to return to England with her where they can live normal lives without the stigma of the scarlet letter attached to her, and without anyone knowing that Dimmesdale is a minister. In other words, Hester seeks a new start for them where she and Dimmesdale and their daughter Pearl can live as a family away from the mores of the Puritan society in America.
As you probably know, the Puritans, as Calvinists, were castigated in England. As a result, they fled to America for their religious freedom. Ironically for Hester and Dimmesdale, it is the strict religion which originally sought freedom that has become a prison for the young couple who love outside the mores of this society. So, in a way, the return to the Old World would again be a flight of freedom for Hester and Dimmesdale. But, once Dimmesdale leaves the forest, he returns to the "prison" of society and, as he is in such a weakened psychological state after living with Chillingworth, he lacks the fortitude to make this new break for freedom.