Sheikh Muhammad al-Sarî`, professor at al-Imâm University in Riyadh
Scholars have expressed various opinions about whether a person who repeats a sin after having repented for the same sin in the past is held accountable for the earlier sin as well.
What seems to be evident – and Allah knows best – is that whenever a person truly and sincerely repents after committing a sin, then that sin is wiped clean away, as if the person never committed it in the first place.
For a person's repentance to be genuine, he or she must feel deep regret for having committed the sin and have a firm resolve to never commit the sin again. These are among the conditions of sincere repentance.
It is not a condition of sincere repentance for a person to be immune from the sin for the rest of his or her life. If the person makes a mistake and falls into the same sin again, this will not revive the previous sin. However, to atone for the present sin, he or she will have to repent for it with sincerity and an equally firm resolve.
And Allah knows best.
Source: Islam Today