Committing adultery is one of the grave sins which is promised evil consequences in this life and the hereafter, but Allah forgives all sins including adultery. He said in the Quran, “Say, O My servants who have transgressed against themselves [by sinning], do not despair of the mercy of Allah. Indeed, Allah forgives all sins. Indeed, it is He who is the Forgiving, the Merciful.” Az-Zumar 39:53)

As long as Allah showered His mercy on you by not revealing what you have kept secret, you should not tell anybody else about it. This is confirmed by the Prophet’s saying to Ma’idah who came and admitted that he committed adultery, “Woe be upon you, go back and ask forgiveness of Allah and turn to Him in repentance.” (Muslim)

According to the version of Abu Dawud “Ma`idh came to the Prophet (peace be upon him) and admitted [having committed adultery] four times in his presence so he ordered him to be stoned to death, but said to Huzzal: If you had covered him with your garment, it would have been better for you. (Abu Dawud) It has been graded as a weak narration).

Based on those reports, scholars maintained that it is recommended that a person does not reveal his sins to people and proclaim his repentance between himself and Allah.

On how should you seek forgiveness from Allah, you have to make a since repentance.

First, your repentance should be meant for the pleasure of Allah. It should not be intended for showing off.

Second,  you must express remorse for the sin you have committed.

Third, you must give up this sin. Fourth, you must have a strong resolute not to make this sin again.

Moreover, you must increase of your righteous and good deeds epically praying in congregation at mosques doing other deeds that draw you closer to Allah. You must also close all cracks and avenues that may give room for the Shaytan such as mingling with women or talking to them without a legal reason.

As for getting married to this person, you must first accept Islam based on your own voluntary will. If you become a Muslim, you can get married to him Islamically by having witnesses and a marriage guardian. Otherwise, a Muslim man is not allowed to get married to any non-Muslim woman except the Jews and the Christians. This is a matter of unanimous consensus among all Muslim scholars.

Allah says what means, “And do not marry polytheistic women until they believe. And a believing slave woman is better than a polytheist, even though she might please you. And do not marry polytheistic men [to your women] until they believe. And a believing slave is better than a polytheist, even though he might please you. Those invite [you] to the Fire, but Allah invites to Paradise and to forgiveness, by His permission. And He makes clear His verses to the people that perhaps they may remember.”  (Al-Baqarah 2:221)

Allah Almighty knows best.