First of all, we’d like to state that Islam prohibits any illicit relationship outside marriage. Islam has taken a firm and decisive stance against Zina (fornication or adultery). Allah, the Almighty, commands in explicit and unequivocal words: “And come not near unto adultery. Lo! it is an abomination and an evil way.” (Al-Israa’: 32)

Thus, Islam not only prohibits Zina, but also closes all the avenues and means leading to it. This is achieved by prohibiting every step and means leading to stimulating desires, opening ways for illicit sexual relations between men and women, and promoting indecency and obscenity.

So, this is a grave sin that requires sincere repentance. one has to fear Allah and stop any relation with this person and to ask Allah for forgiveness. While speaking of repentance, we must hasten to add that repentance cannot be considered valid unless one takes the following steps:
First, one must feel deep remorse for the sins he/she has committed.
Second, one must refrain from the sin totally while also abstaining from all those leads or circumstances that led him/her to such a sin in the first place.
Third, one must be firmly resolved never to sin again and immediately become occupied in whatever good deeds that he/she can in order to wipe out his past sins.