The essence of forgiveness is detailed in various essays on my various websites yet things are not clear to you! Who can help you in the circumstances! Every single human being is master and controller of life... more so the present destiny! Still, we grieve and ponder!
Compulsive thoughts emanate from past life... our residual balance of karma! One can stop inflow of these compulsive thoughts only through indulgence in nishkama karma way of life! By forgiving one and all... we can do away with karma of past lives.
We can get rid of guilt of wrong doings only when whom we wronged forgave us! Who says... we are not the doer? Until we as a soul atman become absolutely pure... we remained the doer! Because of presence of ego... we indulged in wrong doings.
Everything on mother earth, in fact entire cosmos is governed by inscrutable laws of karma. Even God Almighty never interfered with established laws of karma. As we sow so shall we reap... nothing less or more! For every single sin committed by us... we shall get punished as per laws of karma!