I am feeling the urge to cut my son off after he told me that I was not his father.
What was your son's motivation for saying this to you anyway?
I want my son to know I was always there for him, but he doesn't need me anymore.
That sounds painful that he told you weren't his father. Was he brought up thinking you were his father but in fact he was adopted? Or are you his real father but he's disowning you?
I need him to know that he's not my son so I can get away from him.
Just do your best to love him just as a normal father would despite what he is saying. I am sure it is very painful to be told this, however all you can do is proceed to do the best you can. Getting away from him will only make things worse between you two.