All justice has its source in God, the Just Judge. Revenge causes harm for harm, and is contrary to what our Lord teaches. Notice how, if you have ever gotten revenge against someone, your original animosity toward them still exists - even though to a lesser degree? Revenge adds only sin to sin. To take things a bit further, suppose that you never are able to get that revenge say, because the other person moves away. Now, you shall carry that evil desire within you for the rest of your life. So, in essence, that wrong done to you now lives on within you because of your own doing. You have just victimised yourself.
As difficult as it is, we simply must forgive and let go of the wrong done to us. Even more, we are commanded to pray for that person, because whether or not we can stand them, we do know that God loves them. We make ourselves their judge by harboring animosity toward them, when God stands ready to forgive them at the slightest notice. We already know that the other is not a happy person, and that this basic unhappiness affects those all round them. So, pray for their conversion of heart once you have converted your own. Perhaps even before then, since converting our own heart may take a lifetime!.
