Answer
(Fatwa: 688688=M/1430)
Perform two rak?ah salah of repentance and beseech Allah for your forgiveness. Feel regret for what you have done, make firm determination not to commit the sin again and ask forgiveness from Allah. Recall the punishments and torment promised by Allah. Keep yourself away (in purdah) from the relative woman and have no relation with her. Avoid the things as well which lead to the sin. This depends upon your courage and persistent determination. May Allah give you taufeeq to shun the sins.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband