What is the ruling of Islamic law regarding marriage to a young man whom a girl loves, and her family agreed to him, but then turned against him due to sorcery and witchcraft, and how can this situation be handled?

Love between the sexes in universities is forbidden by Sharia due to the impermissible acts it entails. You should repent for what has occurred and cease it. The family's aversion to a suitor might be natural, or due to magic (sihr), or other reasons. If it is highly probable that it is magic, then efforts must be made to treat it. It is recommended to supplicate frequently. Parents should be gently reminded of the importance of prayer in a manner that does not contradict dutifulness to them.