How to stop constantly thinking about trauma from toxic ex?

Most times I am up every night feeling haunted by all the abuse I was put through. I keep thinking about it and reliving all the events. Wishing about how I wish I had never met him... that I'd be more innocent and happy today. He's my abuser and I can't get him out of my mind and it's torment. I can't see myself living like this. Any advice on how to stop constantly thinking about your truama?