Problem with vengeance

What if nothing works? What if someone harmed you so badly that you simply cannot forgive nor forget? If you tried everything. Praying, reading the Scripture, talking to a priest, going on a pilgrimage, confessing, attending Bible study and discussing these matters with other people and still nothing helps. What then?

Even though I'm a lifelong Catholic I didn't know how to answer this when my cousin asked me for advice.

My cousin is a catholic too but he feels like God will not avenge him and even if he does it will not be enough

I told him that our Lord is the ultimate Judge and the He knows best. Honestly it was very difficult for me to listen to these blasphemous words. It is still difficult to say them.

I have been helping and guiding my cousin for months now in the hope that his rage will calm down. Nothing helps. The local culture is also the problem.

We come from a place where revenge is something that youvjust have to do and if you don't do it you lose respect. It's such a silly thing. If somebody punches you should beat them. Older people justify this with the Old Testament. It's so wrong that I am deeply saddened that these things exist.

My place is also known for very traditional Catholicism.

If anyone can give advice I would be grateful my brothers in Christ.

I am not asking if anything is a sin. I don't know why is the note about policy appearing. I hope that this won't be taken down.