Unforgiveness is a very human thing. When we see that something is done wrong against us, there is a barrage of emotions that would flood us. How we handle these emotions is very important. But in the heart of it all, we must decide to forgive--it is not an option, it is a command from God (Mark 11:25).
Forgiveness is a decision, even though we do not "feel like" doing it. We must decide and make up our mind to forgive and only then do we deal with our emotions. So first and foremost, we need to get past our raging emotions to obey and forgive. That is definitely easier said than done - the mind would be raging through all the unfairness, the injustice, the abuse, and the heart would be locked in unforgiveness. It would take time for the mind to unwind and think about it in God's terms (Matt 18:21-35) and be convinced that forgiveness is a must. After which, the heart will have to deal with all the lingering emotions of anger, hatred, and resentment to finally take on instead joy, love, peace, patience, kindness, goodness, faithfulness, gentleness and self-control.
It is not easy, especially when you really see the unfairness and injustice, and you feel that your anger is right. I don't know -- I feel that our anger can be righteous but we are not perfect and our anger cannot be wholly righteous. And even if our anger is righteous, we must not sin or let it last longer than a day (Eph 4:26). We need to be gracious in our anger, and work towards forgiveness.
Time, it takes much time. Healing needs to happen. Issues need to be resolved. There needs to be openness in all parties. But underlining it all, forgiveness has to take place. We are after all, forgiven folks - we are first forgiven by God, and who are we not to forgive others.