Most people who watch porn do so privately and alone - some people might also do it "secretly" but they don't always mean the same thing. At what point was he supposed to announce to you that he was watching porn and wanking? Surely telling you would have made it sound like a much bigger deal than it is, and result in much upset? So you can understand why he didn't when all he wanted was a quick knuckle-shuffle before bed.
Just my opinion but I think it's nice to have some harmless secrets in your life. Not big stuff, affairs etc, just little things that are just for you which no-one can stand in judgment of because no-one knows, whether its a sex toy, some porn, rainy day money or even just a stash of chocolate you don't want to share!
Op, do you hate porn, or do you just hate your man looking at other women? If it's that you hate porn then you need to decide if it's important enough to break up over, or if it's something you can tolerate/ignore.
If it's that you feel jealous or think he prefers looking at the other women to you, then that's a different issue. I think you'd need to explain that to him and see what he says.
Most men who look at porn do it because they like looking at naked women doing rude things. There's not much more to it than that, they aren't sitting there going "God I wish my wife's fanny looked like that!" or "my wife nagged me about putting the bin out again, wish I could replace her with this 18 year old scandinavian girl" they're just thinking "boobs!" - the girl is forgotten as soon as the website is closed.
I think you can ask him to stop looking at porn and give your reasons why, but you can't demand it of him, because you can't enforce it.