Does what transpired between the questioner and the young man fall within the scope of Zina (unlawful sexual intercourse)? How can she atone for this sin? What is the correct course of action regarding this relationship, taking into consideration the potential duration of the marriage?

You must repent to Allah for what you have done, by feeling remorse, seeking forgiveness, refraining from it, and resolving not to return to this forbidden act. It is not permissible for you to establish any relationship with this man who is a stranger to you, even if he is your fiancé. Kissing and touching are not the actual fornication that necessitates a prescribed punishment (hadd), but they are metaphorical fornication and precursors to falling into actual fornication, as stated in the Hadith: "The son of Adam has his share of fornication decreed for him, and he will inevitably attain it. The fornication of the eyes is looking, the fornication of the ears is listening, the fornication of the tongue is speaking, the fornication of the hand is touching, and the fornication of the foot is walking. The heart yearns and wishes, and the private parts either confirm that or deny it." There is no specific expiation for this, but good deeds atone for sins, as Allah Almighty says: {And establish prayer at the two ends of the day and at the approaches of the night. Indeed, good deeds do away with evil deeds. That is a reminder for those who remember.}