Forgiveness is a vitally important piece of following Jesus, and He provided example after example of how and when to do this. Basically, always forgive, period. There are things we think of as unforgivable, but we must forgive it anyway.
Sadly, many of us have a twisted understanding of what forgiveness really is - it means that you decide not to carry anger and judgment against another anymore, and that you are allowing Gods healing and Grace to do it’s work in you. It does not mean that what someone did is OK, and it doesn’t let them off the hook with God or with authorities. It sets your own heart free from bondage. Choosing not to do the tough work of forgiving, is choosing to give someone else power over our own peace. It leads to bitterness and resentment. Choosing to forgive is about faith and trust in God and Jesus, not yourself or someone else.
Forgiveness is not the same as reconciliation either. You can forgive someone without continuing a relationship with them, especially if they’ve been abusive in any way.