This book by Sister Rennee Pittelli was really useful for me in getting through the feelings of of obligation and guilt that I (needlessly) felt burdened and weakened by when trying to understand what No Contact should look like and actually doing it.
I don’t think that it is only good for Christians as much of the guilt and obligation is felt in the same way regardless of religious belief.
There is a great chapter on Rules for No Contact, another on making the decision to break contact, and lots on dealing with flying monkeys and hoovering etc.
I hope this book recommendation is allowed.
GR