I am sorry you are going through this. I was married to a narcissistic sociopath for 18 years and have two children with him. Leaving him was very very hard, as I knew he would do anything to keep control and ruin me.
1) Get legal advice from a law firm that specializes in divorce. Have all your questions written before you go and take a journal with you to write it down. Leave the journal with family or friends.
2) Start planning now because once he knows you want a divorce, your accounts will be frozen and credit cards cancelled. I lived this. When you buy groceries, add a gift card to the bill so you know you can buy food if your accounts aren’t accessible.
3) once you leave, only communicate via email. It will be your record of all discussions and narcissists hate not having control to speak to you directly. I received horrid messages that saved me when we went to trial.
4) move your personal valuables slowly to friends or family, as you won’t have access once you trigger a divorce.
5) start saying personal affirmations at night and in the morning to build your confidence. He will tear you down. I often wondered if I could endure it and was totally broken.
6) buy everything you need for your children for the next year now. My ex refused to pay for anything for our daughters and I wish I had bought everything beforehand.
7) build your network of support. You will get through it stronger and more resilient than ever, but you need shoulders to lean on.

You will be okay. The eye of the storm is the hardest, but once through, the sun shines and you feel worthy again.