learn to dismiss any dark-side thoughts as soon as they enter your head. When dark-side thoughts enter your head, swap them immediately with a favourite worship song. Do this EVERY time. It is in your hands to practise...or not. You can do this.
Lord be with you. x

I strongly suggest you research, Married To A Narcissist. YouTube it too. Being a Christian doesn't mean being a door mat. Lord be with you and give you strength. xxx