porn and masturbation. and cheating

Ok so I have read multiple posts on here about  porn. How people say it's like cheating and it ruins marriages etc. etc.  and I'm just baffled. If you view porn as cheating do you think it's the same when there are sex scenes in movies. Also when people think masturbation is cheating. I really have no words for that. It's masturbatuon is natural. And if you SO is saying that they never masturbate your fooling yourself. Ok rant over. Had to get that off my chest.