You have no obligation to see her anymore. You tried a reasonable visit, and she abused you just as she did during your marriage. Knowing that, it is in your best interest to protect yourself.
Your son is an adult. Living with her, he probably understands your situation. The best solution is to have a relationship and visits with your son completely separate from your ex.
No need to feel bad or guilty about this...you're still newly divorced, and it takes time to sort out how you feel.
Thanks - it was dumb of me to volunteer this visit. It is easy to forget just how bad things were as more time passes. She will no doubt keep up the pressure blaming and shaming. I feel better now I know I am not going. I'm actually looking forward to the drive up to see my son - in secret. Just for a few hours - but have not seen him in 6 months so I feel I must. He actually must want it too as I informed him I would not be coming to the flat and he suggested meeting without her knowledge.
On another note there was something in the news recently - a woman who attacked her husband with a knife and while he was on the phone to the ambulance finished him off by stabbing him in the heart - her words recorded - "I've just stabbed him where his heart should be - but of course he hasn't got one". He died - she claimed he was a controller for 20 years. The man's daughter contradicted that and said it was his wife who was the controller. My wife often accused me of having no heart - she also attacked me with various weapons and came at me with a knife on several occasions. The jury did not believe her and she got 18 years. I feel fairly sure they got it right - it takes a person of zero empathy to stick a knife in someone while he is calling for an ambulance - and controlling NPDs/BPDs really have no empathy at all. I learned that in the 20 years I spent with her.