What is the expiation for what I did after a man proposed to me and we both mutually "gave" ourselves to each other, and he said, "I marry myself to you according to the Sunnah of Allah and His Messenger," and we called upon Allah to witness that, and he kissed me and touched me, and saw from me what a husband sees from his wife, and that happened more than once, then the engagement was broken off?

The woman must repent to Allah and frequently seek His forgiveness, for an engagement does not make the relationship between a man and a woman permissible, and she is not lawful for him except through a marriage contract that fulfills its conditions, including the guardian and two witnesses. The woman should increase her righteous deeds and maintain her obligatory duties, for Allah Almighty says: "Indeed, good deeds do away with evil deeds," and the Prophet, peace and blessings be upon him, said: "Fear Allah wherever you are, and follow up a bad deed with a good one, it will erase it, and deal with people with good character."