What is the ruling on the relationship that developed between me and a young man, and is what happened between us considered a legitimate marriage if offer and acceptance occurred? What is the ruling on his friends knowing about the conversation, and are they considered witnesses? Is it a corrupt marriage that requires divorce? And is it permissible for me to marry now?

You have done well by severing your relationship with this young man and repenting to Allah. You must be careful to avoid any means that could lead you back to that again. Legitimate marriage has its regulations, such as the guardian (wali) and the presence of witnesses. Therefore, it is not permissible for a woman to marry herself, according to the majority of jurists. As for witnesses unintentionally overhearing the marriage agreement, Shafi'i jurists have stipulated the validity of such a marriage. However, marriage is not valid with witnesses testifying over the phone due to the similarity of voices and the unacceptability of a blind person's testimony. According to the Shafi'i school, there is no need for divorce or annulment in a marriage whose invalidity is disputed, but it is more cautious to annul or divorce.