Praise be to Allaah.
If a fornicator repents sincerely, Allaah accepts his repentance. Allaah says (interpretation of the meaning):
“And those who invoke not any other ilaah (god) along with Allaah, nor kill such person as Allaah has forbidden, except for just cause, nor commit illegal sexual intercourse and whoever does this shall receive the punishment.
The torment will be doubled to him on the Day of Resurrection, and he will abide therein in disgrace;
Except those who repent and believe (in Islamic Monotheism), and do righteous deeds; for those, Allaah will change their sins into good deeds, and Allaah is Oft-Forgiving, Most Merciful.
And whosoever repents and does righteous good deeds; then verily, he repents towards Allaah with true repentance” [al-Furqaan 25:68-71]
See also question no. 728.
If he repents, then he may marry a believing woman. If a fornicator repents, he should conceal his past and not spread word of it. And Allaah knows best.