Is the fiancée considered divorced, and is it permissible for her to marry another without my uttering the oath of divorce, or must I utter it?

If, by custom in your country, the gathering, agreement, and recitation of Al-Fatiha are considered a marriage contract, and this occurred with the woman's consent, then it is a valid marriage. It is not permissible for her to marry another man except after divorce or Khul‘. Her marriage to another man in this situation would be adultery.

However, if it occurred without her consent, then it is an invalid marriage (Nikah Fasid), and she has the option to annul it or uphold it. If she chooses annulment and the husband does not agree, she should refer the matter to the Sharia court.

If the custom dictates that what was mentioned is merely an engagement (khitbah) and not a contract, then the marriage has not yet taken place.

Among the pillars of marriage are offer (ijab) and acceptance (qabul). This is when the guardian says, "I give you my daughter in marriage," and the suitor says, "I accept." The contract is concluded by anything that indicates this. Reciting Al-Fatiha during the engagement or contract has no basis [in Islamic law].