I can’t imagine what you have been through since this happened op. Not only did he rape and abuse you, but you were a CHILD at the time.
Can you write it down in a letter to your son - don't hold back on the detail, and explain that any children he goes on to have with his wife to be are at serious risk, and his father isn’t allowed to be around children. Explain to him fully what happened, and tell him you are too traumatised to even tell him in person. You can also do a Clare’s law application. Does your son know he isn’t allowed near children?
You can explain this is why you can only attend the wedding if his father is not there. That as heartbreaking as it will be, having raised him alone, this is not domethhhb that is safe or possible for you to do.
Your son is in denial about who his father really is. I imagine ds was desperate for a father figure, but that does not mean your ds’ feelings should be prioritised over yours op.
There is no way you can attend the wedding, and you shouldn’t have to, that man should not be there, there is nothing stopping you from building a close relationship with your son and his wife after the wedding, and you can enjoy any grandchildren. Everything can be kept separate of course. Your son will need to respect your boundaries around this.
Build a strong relationship with his fiancé if you can, and in time she should know exactly what happened. Especially in order to protect herself and children.
I am sorry this has happened to you. You must feel betrayed and let down by your son’s dismissal of the trauma you have suffered.
You absolutely need to go back into counselling, do you also have others you can talk to? I would suggest counselling for your son too. If your son is close to any one else in the family or family friends perhaps they can also talk to him?
You can carve out this man op. You are certainly not lumbered with him for life. Nor are you obliged to have a close relationship with your son for now if he is determined to ignore what you hsve been through.
The most important person in all of this is you, your son is old enough to take care of himself now.
Take care of you, get all if the help you need to process this terrible development. You come first from now on op 💐💐 Let them get on with it and make their own minds yo when they have all of the facts. It’s ultimately just one day and not worth the fall out in my view. I hope so much that your son wakes up to the severity of this.
Have you considered reporting this all to the police?