What is the religious ruling on a girl marrying someone else despite her intense love for her fiancé and her family's rejection of the latter, and is it permissible for the fiancé to abandon her, and what is the way to identify and invalidate sorcery if the girl's father has been afflicted by it?

Breaking off an engagement is permissible for both parties because it is not a binding contract. However, it is preferable not to break it off without a need. An adult, sane girl has the right to choose her suitable husband, and her guardian is obliged to marry her to him. If the guardian refuses, he is considered to be preventing her marriage (عاضلاً), and she has the right to refer the matter to the judge.

The questioner must sever his relationship with the girl who is engaged to someone else, as she has become a stranger to him. He is not permitted to interfere in her affairs with her family. He must accept Allah's decree and destiny, and seek another girl who is religious and from a good family.