What is the ruling on refraining from marriage due to loving someone with whom marriage did not occur, and feeling that one would be wronging or betraying a future spouse?

The family's decision to reject the religious and well-mannered young man is incorrect, and they should reverse this decision. You should try to forget the young man, look to the future, and pray to Allah to grant you a righteous husband. Your feeling that you will wrong your husband because of your love for someone else is not something a person is held accountable for, as matters of the heart are excused if you fear Allah in dealing with your husband, fulfill his rights, and safeguard yourself for him. This is provided that you do not speak or act upon the love you feel in your heart for another man. A mere heartfelt feeling is a whisper of the self that has been excused, and it is not treachery unless you dwell on it. Whenever this thought crosses your mind, try to repel it and distract yourself from it, while supplicating that Allah turns your heart away from him and instills love for your husband in you.