Also not a doctor! but i am a fellow porn-watcher, and my tastes also run towards the darker side of kinky. i recommend you read what dan savage had to say about that, because it made me feel better. having rape fantasies in the context of a consensual relationship doesn't make you a rapist or a bad person. it's okay to watch porn of stuff that you wouldn't do, it's okay to be turned on by it, and it's okay to play out that fantasy with a consenting partner in a safe way. it's not harming you.