Is the repentance of one who uttered apostasy due to obsessive thoughts, and said, "I don't care if I am a disbeliever" out of despair, accepted, and is his testimony of faith valid if he is still in a state of obsessive thoughts, such that the previous apostate thoughts come to him and he feels that he is not uttering the testimony of faith from his heart?

The door of repentance is always open, and this person should hasten to repent and trust in Allah's mercy. If he said what he said while overwhelmed in his mind, then he is excused and does not disbelieve by that. He should cast away these whispers and strive against himself in repelling them, and know that they do not harm him as long as he dislikes them. It is hoped that he will be rewarded for his striving. He should seek Allah's help and strive diligently in supplication.