Please tell me, can I marry a beliver if I`ve had sex with a non-Muslim? Please answer.
If a fornicator repents sincerely, Allah accepts his repentance. Allah says (interpretation of the meaning):
“And those who invoke not any other ilah (god) along with Allah, nor kill such a person as Allah has forbidden, except for just cause, nor commit illegal sexual intercourse and whoever does this shall receive the punishment. The torment will be doubled for 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, Allah will change their sins into good deeds, and Allah is Oft-Forgiving, Most Merciful. And whosoever repents and does righteous good deeds; then verily, he repents towards Allah with true repentance.”
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 Allah knows best.