I wonder either he is educated at a very low level or has mental issues. I think the moment when he starts to interrupt when you are talking to him or with others, or pokes fun at your stuttering in public, then it's fking time to kick his ass. Don't repress your angers and hatreds man. In addition, I saw that you can experience your vocal cord closed up when you stutter. I think you can try speaking with a lisp from now on to reduce the tensions forced onto your articulators due to neurology and if you still can't visualize what speaking with a lisp is going to be like, you can check my last post about Gentle Speech. I even exemplified Fenster in <The Usual Suspects> who is typical of speaking with a lisp for my illustrations and hope I can help you a lot :).