I don't know if this helps, but my youngest brother says there are four levels of forgiveness:
- letting go of the pain the person caused you,
- developing compassion and understanding toward that person,
- doing something nice for that person,
- trusting that person again.
The problem with that last (fourth) level is that the person who hurt you has to take action of their own to help restore the trust. And, you must provide for them a series of reasonable steps they can follow in order to get your trust back.
So, we don't always make it through all four levels of forgiveness. But we can usually get through the first three.
How many levels of forgiveness can you do for your ex? What would you need to make that possible?
Maybe approaching forgiveness in light of those levels would help you to get some closure. Who knows.