I personally was gaslighted by my abusive mother from age 3 until 17. She is still alive and I am estranged from her. Gaslighting in my opinion is the most cruelest form of torture. To make it where the victim can not even find refuge within themselves. They make you question your own sanity, question what you think is normal and what is not, question your innocence. This all occurring in my formative years scarred me for life when my only crime was simply being born.

First I need to recommend professional therapy. It is expensive, but if you can afford it take advantage of it.

In your case you need to acknowledge that you are no longer in the abusive relationship. That is now in the past. When healing yourself you need to see the importance of the present moment. The present moment is the only time healing takes place. Realize that the past is over and the furture is not here yet. Your abuser was hard on you. Sometimes we tend to be just as hard on ourselves as our abusers were. Self compassion and self love is going to be very important on your path to healing (and you will heal). You may also utilize cognitive behavioral therapy (CBT) to deprogram any distorted thinking you may have developed.

As a grown man in my 30s, I still was struggling from abuse that happened in my childhood until I made a conscious effort to move past it. I am more than confident you will get past this. I will share with you what has helped me. I hope it helps you.
My regiment:
-professional therapy (when I have the luxury to afford it)
-exercise daily
-daily meditation (I often practice with Buddhist monks and nuns)
-staying fully present in the moment

Books that helped me:
For CBT to retrain negative and distorted thinking, this book is top rated.

For regaining self esteem and self worth this book helps me.

For any depression you make have encountered