All perfect praise be to Allah, The Lord of The Worlds, and may His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
Repentance from sin is an obligation on every Muslim man and woman for Allah, The Almighty, said: " And rally to God in repentance, O believers, so that you might be prosperous. "{An-Nur/31}.
Conditions of repentance are:
1-Showing remorse.
2-Quiting sin.
3-Determination not commit that sin again.
Please refer to the book entitled {Fateh al-Bari}. A fourth condition is added to the above, and it is about giving back rights to whom they belong. Therefore, whoever committed a theft or usurped a wealth must give it back to its rightful owner or ask for their forgiveness.
The Messenger of Allah(PBUH) gave glad tidings to the repentant where he said: "The one who repents from sin is like one who did not sin."{Ibn Maja}
Moreover, committing the same sin over and over again shouldn`t prevent one from repenting. In fact, repentance is all about being determined not to commit the same sin again, but it doesn`t mean not falling into it. Therefore, if he fell in that sin again, it doesn`t annul his previous repentance, but that repentance should be renewed.
Narrated Abu Huraira: I heard the Prophet (PBUH) saying, "If somebody commits a sin and then says, 'O my Lord! I have sinned, please forgive me!' and his Lord says, 'My slave has known that he has a Lord who forgives sins and punishes for it, I therefore have forgiven my slave (his sins).' Then he remains without committing any sin for a while and then again commits another sin and says, 'O my Lord, I have committed another sin, please forgive me,' and Allah says, 'My slave has known that he has a Lord who forgives sins and punishes for it, I therefore have forgiven my slave (his sin). Then he remains without Committing any another sin for a while and then commits another sin (for the third time) and says, 'O my Lord, I have committed another sin, please forgive me,' and Allah says, 'My slave has known that he has a Lord Who forgives sins and punishes for it I therefore have forgiven My slave (his sin), he can do whatever he likes."{Related by Bukhari}.
An-Nawawi(May Allah have mercy on him) said: "If a person committed a sin for a hundred times or a thousand times or more and repented for every time, Allah forgives him and his sins are erased. Moreover, if he made repentance for all the sins that he had committed then it is also acceptable.{Shareh An-Nawawi Ala Muslim, 17/75}.
Ibn Daqeeq(May Allah have mercy on him) said, "If a person would commit the same sin again and again in one day and made repentance as it should be-fulfilled all conditions of repentance- then Allah forgives him"{Shareh al-Arba`een An-Nawawiah Li Ibn Daqeeq Al-Eid, p.138}.
Moreover, a Muslim should trust in Allah since He, The Almighty, accepts acts of worship from His slaves as well as the repentance of the repentant. He said, " Say [that God declares]: ‘O My servants who have been prodigal against their own souls, do not despair of God’s mercy. Truly God forgives all sins. Truly He is the Forgiving, the Merciful."{Az-Zumar/53}. He, The Exalted, also said: " And He it is Who accepts repentance from His servants, and pardons evil deeds, and knows what they do."{Ash-shura/25}. In addition, Prophet Mohammad said: "Allah, the Exalted, has said: 'O son of adam, I forgive you as long as you pray to Me and hope for My forgiveness, whatever sins you have committed. O son of 'Adam, I do not care if your sins reach the height of the heaven, then you ask for my forgiveness, I would forgive you. O son of 'Adam, if you come to Me with an earth load of sins, and meet Me associating nothing to Me, I would match it with an earthload of forgiveness."'{At-Tirmizi}.
We advise the questioner to adopt means that help him make sincere repentance, such as getting rid of bad companions and keeping company with the righteous for Allah, The Almighty, said: "And restrain yourself along with those who call upon their Lord at morning and evening, desiring His Countenance; and do not let your eyes overlook them desiring the glitter of the life of this world. And do not obey him whose heart We have made oblivious to Our remembrance, and who follows his own whim, and whose conduct is [mere] prodigality."{Al-Kahf/28}. And Allah knows best.
