'Ask him why he needs to look at porn in order to masturbate, the answer is, he doesn't. He could masturbate in bed, beside you/with you helping FFS!'
Unless this was part of a mutual sex session, I would find this really creepy/exploitative.
Sometimes, DP feels horny and I don't. He goes and has a wank surreptitiously. Sometimes it's the other way round and I'm equally surreptitious. I'm not sure either of us even could do it if the other one was just lying there, not particularly into even watching.
WRT porn, the way I look at it is that some people have wonderfully vivid imaginations that never let them down and some occasionally need pictures or words to help them along. There are obviously some serious issues around the way porn is produced but if there was such a thing as 'fair trade porn' I personally wouldn't have a problem with it. And yes, IME, most men admit to looking at it at least occasionally.
However, if porn use at whatever level is getting in the way of a happy relationship, it really needs talking about. I think men probably are different to us in some fairly basic ways, but not that different - most of them want happy, close, honest relationships, just like us, and are prepared to compromise a bit to make that happen.