Anger over injustice

The situation angers me to this day, and yet it did not concern me in any regard. One ex-close friend lying and betraying another close friend. Showing no remorse and getting away with her actions. Injustice always hit me to the core and always manages to spark within me an unknown sudden surge of energy and anger surprising all around me. Every smile and loud gales of laughter she gave within earshot added further fuel to my already simmering internal pressure cooker. How do people like this exist in the world lord? Who walk around acting blissfully unaffected and happy having lied and caused so much pain to a formed friend who worshipped them? How do they sleep at night? How do they live with themselves? How do they have the courage and faith to act falsely oblivious to the world? How? How?
How can I walk around letting them get away with their actions having faced no consequences on top of causing further grief?
Or better yet, how God do you expect me to have the strength to deal with individuals as such and not get involved?
How should you act towards those who are either so mentally ill they are unaware of their own actions or those to the other extreme who are so manipulative and of an unsound mind that they can be considered to be a psycho?

Should you be compassionate? Should you just work hard to maintain your own feelings and be mature regardless of your feelings surrounding the situation?

I know my actions and behaviours throughout the period added nothing to help the situation nor quell my anger except give brief moments of triumphs of revenge. I know my actions were childish in nature but at the time I felt that I could not carry on without getting myself involved to almost remedy the injustice that was occurring even though I had nothing to offer except a show of anger and violence to intimidate the opposition.
Others called me brave to get involved in a situation not my own. I was not trying to be show that I was courageous. I know that it was my own strongly held emotions regarding injustice and anger that were getting the better of me.
I wish I could have been stronger and not let my feelings run away with me. I wish I did not carry out acts of harassment such as verbally tormenting her although I felt at the time that she gave me no choice. Causing another grief did not give me the relief and victory over injustice that I was hoping it would. Causing her grief almost added salt to my own wound, making me feel more guilty over my own acts.

What right do I have in fact, to play God and battle the woes of others? Why does injustice and the ill behaviours of others always invoke such strong waves of anger and energy within me? Why do I assume that verbally tormenting those who have done wrong will somehow intimidate them into submission? Why do I think that I am some guardian of my loved ones?- an arrow to them somehow simultaneously wounds me too

I can only pray that God will give me with time the courage and patience to deal more wisely with those who have done wrong to my loved ones. For I can see that my actions had no positive impact on the situation. In future taking a step back and not let my emotions overcome my logical mind. Religious texts say love thy enemies, but how do you put this into practice? How? How do you love those who you feel are so mentally ill and not worth your time or friendship or space on earth?!! God knows all, and this may be my greatest challenge yet, to overcome and be in control of my own emotions and to not let my pride and sense of righteousness get the better of me!
Hurting thy neighbour, hurts yourself.

"Holding onto anger is like holding onto fire is like grasping a hot coal with the intent of harming another; you are the one who gets burned!" Buddha