I’m looking for a self help book about leaving relationships.

Hi guys. I'm really looking to find a book to help me get the courage to leave a long term relationship and start over while being a codependent person. A little context: my boyfriend is a narcissist, a recovering alcoholic that has had many a relapse, and our relationship is no longer good for me mentally. It's putting a lot of stress on me, to the point it's affecting my career. I've wanted to leave, but I have never been good at leaving a relationship. I unfortunately thought I could fix him for the first few years, but I've realized it's not my job to fix someone. So someone, please reccomend me some books to help me put a plan into action.