Islam guides in Truth that regardless of the number of times one falls into temptation and commits a sin, as long as one sincerely turns back to their Lord seeking sincerely forgiveness, the Lord Most Gracious Most Merciful has promised to forgive that repentant slave his sin.

Allah says in the Holy Quran Chapter 39 Surah Zumur verses 53-54:

(O Prophet) say: “O My servants who have wronged their own souls….Do not despair of Allah’s Mercy!  Surely,  Allah forgives all sins.   He indeed is the All Forgiving,  All Merciful.   Return to your Lord and submit to Him before the scourge overtakes you;  for then you may get no help from anywhere.”

Allah says in the Holy Quran Chapter 3 Surah Ale Imraan verse 135-136:

Allah likes such good people very much, who,  if ever they commit a base deed or wrong their own soul by the commission of a sin,  remember Allah instantly,  and ask for forgiveness from Him for their shortcomings.  For who,  but Allah,  can forgive sins?  (And Allah loves those) who do not knowingly persist in the wrongs they did.   These will be rewarded with forgiveness from Allah,  and with Gardens beneath which canals flow,  and they will reside therein forever!   How excellent is the reward of those who do good deeds!

Allah says in the Holy Quran Chapter 6 Surah Anaam verse 54:

When those come to you who believe in Our Signs,  say: "Peace be on you!  Your Lord had inscribed for Himself (the rule of) Mercy.  Verily if any of you did evil in ignorance,  and thereafter repented and amended (his conduct),  Lo! He is Oft-Forgiving,  Most Merciful."

Sahih Muslim Hadith 6499     Narrated by Abu Dharr

Allah's Messenger (saws) said: that Allah, the Exalted and Glorious, stated: 'He who comes with goodness, there are in store for him ten like those and even more than those; And he who comes with vice, it is only for that that he is called to account. I even forgive him as I like, and he who draws close to Me by the span of a palm I draw close to him by a cubit, and he who draws close to Me by a cubit I draw close to him by the space (covered) by two hands, and he who walks towards Me I rush towards him, and he who meets Me in the state that his sins fill the earth, but not associating anything with Me, I would meet Him with the same (vastness) of pardon (on My behalf)."

Hadith Qudsi 34

The Messenger of Allah (saws) said that Allah Subhanah, High and Exalted He is, says: ‘O son of Adam, so long as you call upon Me and ask of Me, I shall forgive you for what you have done, and I shall not mind.  O son of Adam, were your sins to reach the clouds of the sky and were you then to ask forgiveness of Me, I would forgive you.  O son of Adam, were you to come to Me with sins nearly as great as the earth and were you then to face Me, ascribing no partner to Me, I would bring you forgiveness nearly as great at it.’

Al-Tirmidhi Hadith 2339        Narrated by Abu Sa'id

Allah's Messenger (saws) said that the Shaytaan said, "By Thy Might, my Lord, I shall continue to lead Thy servants astray as long as their spirits are in their bodies."  The Lord, Who is Great and Glorious, replied, "By My Might, Glory and Exalted Station, I shall continue to pardon them as long as they ask My forgiveness."

Ahmad transmitted it.

Thus one who sincerely believes in the vastness of the Lord’s Grace and Mercy, should never never ever despair of the Mercy and Pardon of His Lord, regardless of what or how many sins one might have done in one’s past…..if one sincerely turns back unto the Lord seeking His forgiveness, he will find his Lord Forgiving and Merciful.

But those sinners will not be forgiven who pre-plan to commit sin with the intention that after they have sinned they will seek forgiveness; then pre-plan the sin again with the intent that they will repent later, or persist in their sin with the intent that they will seek repentance just before their death…..such sinners try to make a mockery of the Vastness of the Mercy and Grace of the Lord Most High with their pre-planned sinning and meaningless repentance.

Allah Says in the Holy Quran Chapter 4 Surah Nisaa verses 17-18:

17      Allah accepts the repentance of those who do evil in ignorance and repent soon afterwards; to them will Allah turn in mercy; for Allah is full of knowledge and wisdom. 

18      Of no effect is the repentance of those who continue to do evil until death faces one of them and he says "Now have I repented indeed"; nor of those who die rejecting faith: for them have We prepared a punishment most grievous.