So I know a guy who has committed these things and now he's asking me will he has to marry that girl in the future cause he has seen in Sur'ah an nur that if fornication takes place the girl has to marry a mushrik and the boy would have to marry a mushrika. Now he's question is ...will this be Zina? And can they marry anyone they wants to? Or they will have to marry themselves only?
Kissing and doing lustful actions to someone that is not your spouse is not zina in the popular definition of zina which is unlawful sexual activity involving the private parts outside of marriage. But these are actions are still considered to be sinful, zina of the mouth, and zina of the other body parts that were involved.
Narrated Ibn `Abbas: I have not seen a thing resembling 'lamam' (minor sins) than what Abu Huraira 'narrated from the Prophet who said "Allah has written for Adam's son his share of adultery which he commits inevitably. The adultery of the eyes is the sight (to gaze at a forbidden thing), the adultery of the tongue is the talk, and the inner self wishes and desires and the private parts testify all this or deny it."
Can a fornicator marry a believer
The ayah you are referring to is Quran 24:3
According to Tafsir Al-Jalalayn, this ayah was abrogated by 24:32:
[24:3] The fornicator shall not marry anyone but a fornicatress or an idolatress, and the fornicatress shall be married by none except a fornicator or an idolator, in other words, what is suitable for each of the two [for the purposes of marriage] is the above-mentioned; and that, namely, marrying of fornicators, is forbidden to believers, who are better [than those]. This was revealed when the poor among the Emigrants resolved to marry the wealthy whores of the idolaters, so that they [the women] would provide for them. Thus it is said that the prohibition applies Specifically to them; but it is also said to apply in general; but it was abrogated by God’s words: Marry off the Spouseless among you [Q. 24:32].
According to Tafsir Al-Kareem Al-Rahman, it is okay to marry them as long as they repent and are not characteristically committing fornication:
(Such marriages are forbidden to the believers!) that is, Allah has prohibited them to marry fornicators. What this verse means is that if a person - man or woman - characteristically commits fornication, and does not repent from it, the one who wants to marry such a person, despite the fact that Allah has forbidden that, must either not be adhering to the rulings of Allah and His Messenger, and such a person can only be a polytheist; or he or she is adhering to the rulings of Allah and His Messenger, but goes ahead with this marriage despite being aware of the other person’s fornication. In that case, the marriage is fornication and the individual is a fornicator and is immoral, for if he truly believed in Allah, he would not do that. This clearly indicates that it is prohibited to marry a woman who fornicates unless she repents, and it is prohibited to marry a man who fornicates unless he repents. That is because the connection between a husband and wife is the strongest form of companionship and bonds between people.
So if that gentleman you're speaking of repents sincerely and mends his way (gives up zina) then he can marry another woman (as long as she's a believer or people of the book) besides that woman that he committed zina with.