What is the ruling of the Sharia on a fiancée returning to her fiancé after the engagement was broken due to family interference?

There is no harm for a man to propose to a woman as long as she has not been proposed to. Your mere intention and desire to propose to her are not sufficient.

As for your friend lying to you, that is forbidden. The Prophet, peace and blessings be upon him, said: "If what you said about him is true, you have backbitten him; and if it is not true, you have slandered him." He must repent and seek your forgiveness. It is not good companionship for your friend to propose to a girl knowing of your desire to propose to her. You should turn your attention away from her and seek someone else.