I am going to come at this from a different angle. You say you need to forgive him for your own sake but is it possible you can heal without forgiving him, at least for the time being.

I found this article you might find helpful:
Why You Don't Always Have to Forgive | Psychology Today UK

I personally would stay open minded about forgiveness, if you feel it then okay but pressuring yourself to forgive him doesn't seem fair to yourself. Is it possible you can learn to heal without forgiving do you think?