Hi Golden_eve, this is a very hard question.
I'm just going to put down some thoughts, I have no answers, living is too messy.

Sometimes I feel I have more idea what forgiveness is NOT rather than what it is.
It is NOT pretending to feel that everything is ok and that you no longer feel hurt.
It is NOT keeping up contact with someone if they deliberately make you suffer.

The problem is that nurturing and feeding resentment and anger will do little more than make you feel awful and grow a stomach ulcer. It harms you and not the perpetrator.
However, you have the right to feel what you feel. Your emotions are for a good reason and you need them.

I like to think of letting go of what the abuse has told us about our worth as a human being which is all lies. The adviser wants you to feel worthless and bad.
You are unique and valuable. You're a human being and therefore precious.
You are strong, or you would not be here reaching out.

If you are out of the abusive situation and you are an adult then in theory though can choose more healthy relationships and choose how you live and who you speak to.

Maybe the unforgivable cannot be forgiven.

Maybe there is a way to let go of bitterness but still be honest that harm was done.

Maybe there is a way to live with the mental injury and look to build a future where that is NOT the important thing about you.

Think of someone who got beaten up armed now walks with a limp. They limp because they hurt but they still try to live as well as they can and do normal things. They can't do everything because of the pain but if they worry about the beating they get more scared and can't do anything. If they go out, with help if they need it, they can make a new life.
The new life is affected because they are hurting but limping is not the most important thing about them and their energy goes more into life than thinking about being beaten.

I feel like I'm writing rubbish because it is so hard to put into words.

All I know is that it is so very very hard to do but also that resentment and revenge/vengefulness makes us sick, physically as well as mentally.

One thing that helps me is to keep repeating to myself that I'm ok (which for me means not evil). I might say "I'm good" but I find that's too hard.
Reminding myself all the time that I'm "good enough" helps me not to focus so much on what I'm feeling about the past. And I may feel a little more able to look forward.

Please understand this is not"the answer" to your question, just some thoughts on an almost impossible question meant kindly.

Be kind to yourself if you can, YOU'RE worth it.