I know the person who I'm talking about really well too. I've known him for years and I've had a few bad dreams where the other version of himself attacked the other version of myself. Was I scared? Yes. Do I think about it still? Yes. Do I blame the man I've known forever? No.
Like I said, it doesn't hurt to be a little cautious, but at the same time, don't just write someone off because of what happens in the dreams. Shutting someone out because of that could be worse, especially if staying close or being there for them is what prevents them from becoming something terrible.