How can one mend oneself and repent sincerely to Allah from repeated fornication, given the fear of the torment of the grave and the impact of sins on deceased parents, coupled with feelings of distress and remorse, and a desire to return to Allah?

You are in grave danger by persisting in the abomination of adultery, exposing yourself to Allah's wrath and punishment. Hasten to sincere repentance to Allah, and help yourself by marrying, for it is the best safeguard for one's chastity. If you are unable to marry, then you must fast and keep the company of the righteous. Stay away from everything that incites your desires and from those who advocate immorality. Adhere to the mosques, circles of remembrance (dhikr), and gatherings of knowledge. Be sincere to Allah and strive in supplicating Him to avert evil and indecency from you. Frequently remember death and its horrors, and fear Allah's punishment. Hasten to sincere repentance and have a good opinion of Allah, for He is the Forgiving, the Merciful, and He will forgive you if you repent and abandon abominations.