What is the ruling in Islam on concealing the name and identity of someone who backbit about me and caused me harm, and am I entitled to know who it is? What is the ruling on someone who informs me of their identity?

Matters unfold according to divine decree. What was destined to befall you could not have missed you, and what was destined to miss you could not have befallen you. If the engagement was broken, be patient with what Allah has decreed, and know that it is good and in your best interest, and that all of Allah's decrees are good. Surrender to Allah's judgment and choice, for His choice for you is better than your own choice for yourself. What you believe to be backbiting might be an illusion, so do not preoccupy yourself with it and do not harbor ill thoughts about people. Turn to obedience to your Lord, have good expectations of Him, and strive in supplication that He may decree what is good for you. Even if backbiting was the cause, your right will not be lost. Stop thinking about what has passed and do not search for the reason behind what happened, for that will only lead to more exhaustion.