Are kissing and touching considered adultery (zina), and is the woman who commits them considered an adulteress (zaniyah) cast out from the mercy of Allah? What is the expiation for that, and how can a woman regain her chastity and self-confidence after these acts?

Man is not infallible; however, "the best of those who err are those who repent." What is required is sincere repentance to Allah, with its conditions: remorse, abstaining [from the sin], and resolving not to return [to it]. Through repentance, Allah erases sins and pardons misdeeds. The sins that occurred with the young man are expiated by sincere repentance and by cutting off the relationship with him until a legal marriage contract is concluded, as engagement does not make the unlawful lawful, and an engaged man is still a stranger [to the woman].