Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
If this man repented sincerely to Allah, Allah will accept his repentance. He promised this as he says: "And He it is Who accepts repentance from His slaves, and forgives sins, and He knows what you do. (Ash-Shura 42:25)
Allah also says: "And those who invoke not any other ilâh (god) along with Allah, nor kill such life 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 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, 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. (Al-Furqan 25: 68-71)
Furthermore, Imam Muslim reported in his Sahih that Abu Hurairah, may Allah be pleased with him, narrated that Prophet (Sallallahu Alaihi wa Sallam) said: "Whoever repents before the sun rises from the west, Allah will accept his repentance."
So, this man has to do well in the future and perform good deeds as much as possible, and he should not return to this again. He should not despair of the mercy of Allah, as Allah says: "Say: "O 'Ibâdî (My slaves) who have transgressed against themselves (by committing evil deeds and sins)! Despair not of the Mercy of Allah, verily Allah forgives all sins. Truly, He is Oft-Forgiving, Most Merciful. "And turn in repentance and in obedience with true Faith (Islâmic Monotheism) to your Lord and submit to Him, (in Islam), before the torment comes upon you, then you will not be helped. (Az-Zumar 39: 53-54)
So, Allah forbade us to despair of His mercy and ordered us to repent. This is the only correct solution for whoever has committed a sin. He should know that as long as he repented, he is not obliged to acknowledge this sin so that he will be punished. In addition to this, he should not inform anybody else about it; he should conceal his sin.
Imam Malik reported in Al-muwata' that Zaid Ibn Aslam narrated that the Prophet (Sallallahu Alaihi wa Sallam) said: "If anybody has committed any filthy sin, he has to conceal himself with the screen of Allah."
As regards your order to him to fast 60 days, the Shariah has not legislated this, and he is not obliged to do so. What he should do is to multiply the good deeds, like fasting and so on. And this is not an obligation.
Finally, we remind you that this man is still an alien to you, and it is not permissible for both of you to stay in seclusion at all, and he should not talk to you except when there is a need and without being in seclusion. Nevertheless, there is no harm, InshaAllah, for him to marry you, as long as he repented.
Allah knows best.