Trust your gut instincts. This guy's behaviour seems strange. I feel he's up to something. Be firm with your boundaries. You can't even block him if he's not on Medium, and by the sounds of it, if you did, he would create a new account. I don't get a good feeling about what your telling me. Unless you really need to deal with him, I would cut off contact. Be confident in yourself. You've a right to express your feelings and thoughts. Don't let him undermine that.