All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
Whoever informs others of committing Zina (fornication or adultery), whether he is a mufti or someone else, it is not an obligation to implement the Hadd (i.e. the corporal punishment determined by the Islamic Law) on him unless he confesses with his act before the ruler with the conditions that should be met for such confession; in which case, the Hadd punishment is executed on him.
Since the person has repented to Allah from his sin, then his repentance is accepted and he will be like someone who has never sinned as the Prophet said: “A person who repents from sin is like a person who has never sinned.” [Ibn Maajah]
It is permissible for him to marry whomever he wants from among the chaste Muslim women, and he must strive to do righteous deeds because good deeds remove bad ones, and he must keep away from every environment that would lead him to that sin again.
Allah knows best.