How can a person who has sinned and repented, and been forgiven by the one he wronged, be convinced that he should not punish himself severely (such as by not marrying and halting his life) after his repentance, but rather that he should overcome his feeling of guilt and forgive himself?

The wrongdoer must repent to Allah and seek forgiveness from those he has wronged, and he must increase in good deeds that expiate sins, such as prayer, for Allah the Almighty says: "Indeed, good deeds do away with ill deeds." (11:114) And for the saying of the Messenger of Allah, peace and blessings be upon him: "Fear Allah wherever you are, and follow up a bad deed with a good one, it will erase it."

As for refraining from marriage or anything that harms oneself, it is not permissible, because "there is no harm nor is there to be harm" in Islam. If this is done out of religious devotion, it is considered a forbidden innovation (bid'ah), because a Muslim is commanded to worship Allah according to what He has legislated, not according to what a person invents. Repentance and performing good deeds are what Allah has legislated for sins. Whoever is not content with that has innovated in religion. Al-Shatibi said: "Innovation is an invented way in religion that resembles the legitimate way, and the intention behind following it is the same as the intention behind the legitimate way." Whoever deprives himself of what is lawful without a legitimate excuse has turned away from the Sunnah of the Prophet, peace and blessings be upon him, and one who acts contrary to the Sunnah out of devotion is an innovator.