St. Celestine had to be DRAGGED out of his cave, he had no wish to be made Pope. His abdication is not even remotely suspicious. They say Boniface shut him up in some tiny little cell but it sounds to me like that's what the ascetic Celestine wanted.
Or maybe Boniface killed him. But as Catholic Martyr said, the immorality of a Pope does not make him a heretic. Pope Vigilius before becoming Pope was said to be involved in a murder... Of a Pope! He defended the Monophysites against the Catholics. THen hen he became Pope, he reversed himself completely. The Holy Spirit guided him and he went to war with the Monophysites. The same process happened with Pius IX who was quite liberal before becoming Pope, and then changed, the great responsibility of the Office impressing truth on his soul.