Is it permissible for a woman who is engaged to leave her fiancé and wait for another person towards whom she has developed feelings of love, and who reciprocates the same feelings?

You must fear Allah and stay away from contact with this man, because he is a stranger to you. You must be content with what Allah has destined for you. It is not permissible for you to propose to him for yourself or for anyone else, because he has committed to another fiancée. The Prophet, peace and blessings be upon him, forbade proposing over the proposal of a Muslim brother. The scholars have unanimously agreed on the impermissibility of this after acceptance and commitment, unless the suitor leaves his fiancée or gives permission for someone else to propose.