Your facts are very compelling and my heart really goes out to you. You have set a new course for your life and your children are very lucky.
Your goal is to do what is best for your 8 year old of course and you want to prevent him from being hurt by a father who has only been a father in name for some time.
It is very hard to convince a court to sever all rights of a parent.
So the court is likely going to want to restrict access but not cut off all rights.
One compromise is to only have supervised access and that would be where a professional agency does the supervision.
But if that is going to be harmful then you would have to prove to the court that any contact with the father is not going to be in your child's best interests.
You may need to bring in a professional to do an assessment and provide a report for the court.
So your next step should be to retain a family lawyer in your city who can then seek the order you need or at least assist you in getting that assessment done first.
Does that help as a starting point?
Please feel free to post back with any follow-up questions you may have. If you don't have any then I hope I have earned a 5 star rating but if you don't feel that I have please don't hesitate to reply back and let me know what more I can do to assist you. Finally, please know that even after you rate me I will be here for you and you can ask follow-up questions if you think of them later on at no further charge of course.