Muslim man who has  relationships with non-Muslim women
Question

                What is Allah advise to a Muslim married man who has had several relationships with non-Muslim girls and even had sex after marriage, with ex-girlfriend
Praise be to Allah.Zinaa (unlawful sexual activity, fornication/adultery) is one of the major sins, concerning which Allaah and His Messenger issued a stern warning. Allaah has warned the one who does this of a painful torment, and has stated that it is an immoral action and an evil way. This person has to repent and seek forgiveness. His repentance will not be valid unless he gives up this evil action, regrets what he has done in the past and is determined never to do it again. Zinaa on the part of a married man is worse than zinaa on the part of one who is not married, hence the punishment for a married person who commits zinaa is stoning to death. He should know that Allaah says (interpretation of the meaning):
“And all of you beg Allaah to forgive you all, O believers, that you may be successful” [al-Noor 24:31]. And according to a saheeh hadeeth: “Repentance wipes out that which came before it.” Let him hasten to repent and turn to Allaah. May Allaah help him to do that and to reform himself.