What is the ruling on saying "I am an unbeliever" unintentionally due to extreme distress and obsessive thoughts? And what is the ruling on discussing the verse "And He knows what is in the wombs" with others despite obsessive thoughts? And how can one get rid of the feeling of hypocrisy and weakness of faith? And how can one repent after returning to sins despite prior guidance?

If disbelief (kufr) issues from you in a state of extreme emotional agitation and absence of reason, then there is no sin upon you because the Pen has been lifted from the insane. However, if the discussion was about a Quranic verse without knowledge of its meaning, then this is a grave error that necessitates repentance and seeking forgiveness. As for what you feel of whispers (waswasa) or a sense of hypocrisy, that is from Satan, and sincere repentance and seeking forgiveness suffice you. To overcome despair and anxiety due to not remaining steadfast in righteousness, it is recommended to frequently supplicate (especially, "O Turner of hearts, make my heart firm upon Your religion"), to keep good company, to avoid temptations, to utilize time beneficially, and to persevere in seeking forgiveness and repentance.