You probably should stop 'reading' and researching. You had an exposure years ago and have tested years later and do not have HIV. You've been reassured this at least two times that I read above by health care workers. So, you need to let it go. Get some help with anxiety if you find you can't.
This sounds like a psychiatric problem. You have tested negative and don't have HIV dementia. They do not believe you because it's not true or reality. I would seek help in the area of your thinking rather than trying to diagnose yourself with "aids". I say this with compassion because you won't move past this until you focus on the true problem. Therapy would give you a place to talk about it.
You are not going in to the story books, let's face it, you and I we both know deep down that you don't have HIV.
Undetected RNA and a negative western blot has every thing done and dealt.
You will perhaps fall sick many times during the course of your whole life, you can't possibly relate it to an event that happened 8 years ago. The irony is, your exposure as you describe also seems uncertain, it was most likely not even an actual one.
You have issues that need attention of a psychologist, please see one to overcome it. You don't have an HIV concern.
We wish you the best.