Does God forgive the sin of a woman who exposed her body to a young man online, then repented, and now wishes for this person to stay away from her, and for God to take her right from him? And are there supplications that keep evil people away?

You have done well by repenting of the sin, and the completeness of repentance lies in immediately cutting off all ties with this young man. Have a good opinion of your Lord and trust in His forgiveness, for He says: "And indeed, I am Forgiving to whoever repents, believes, and does righteousness, and then is guided." (Taha:82).

If you repent and fear Allah, He will conceal your sins in this world and the Hereafter, "And whoever fears Allah – He will make for him a way out." (At-Talaq:2).

If you fear the evil of this young man, supplicate with the prophetic supplication: "O Allah, we place You in their throttles, and we seek refuge in You from their evils."

And if you were obedient to him, you have no right over him, and perhaps Allah will transform your bad deeds into good deeds through your repentance: "Except for those who repent, believe and do righteous work. For them Allah will replace their evil deeds with good. And ever is Allah Forgiving and Merciful." (Al-Furqan:70).