confusedmum, I think I know how you feel, a bit, a similar-ish thing happened to me and I wrote down how I felt about it at the time. Here it is:
"If you read ?I caught my boyfriend wanking over porn on the internet? in a magazine problem page what advice would you give? I would probably have said: ?So what? All men do it, it doesn?t mean they love you any less, he wasn?t being unfaithful with a real woman, it?s only porn; ignore it or join in, depending on where you stand on porn in general. Come on woman, this is the twenty first century!? Until now. Because this happened today and I didn?t react that way at all.
We know that life in the problem pages doesn?t always accurately reflect real life, but when this happens to you the reality is awful and shocking and sad. Maybe some background is useful here: my husband and I live together. He is intelligent, articulate, professional and handsome. Not to mention extremely sexy. Not your archetypal dirty mac brigade, or sorry bachelor. And our sex life is great, always has been. So why did he need to do it, and, more to the point, why was I so shocked? Well, for one I didn?t like the fact that he was unpleasantly surprised to see me home early, rather than thrilled to see me. And I was therefore caught in cliché: girlfriend or wife alters her plans, discovers something she didn?t want to know, everyone?s unhappy.
Although I don?t necessarily object to porn per se, because I haven?t sorted out where I stand on that thorny issue, I objected to this, big time. If it had been a pornographic magazine, maybe I?d have felt differently, who knows? But it wasn?t. There is something seedy and sordid and almost tragic about seeing a grown man, naked and fully erect, hunched over a computer frantically scrambling to close whatever is on the screen in front of him. Something he doesn?t want you to see. And although you know damn well what it must be, because what else could you possibly object to? it is still shocking. Especially if you heard a low moan as you walked up the stairs and assumed it to be the sleeping mumbles of your lover.
So why is it shocking? Maybe because, although women have a sex drive too, most wouldn?t use internet porn to express it. There may well be porn on the internet for women, but I wouldn?t know because it hasn?t occurred to me to look. My guess is that most internet porn is by and for men, just as it is on the newsstands. Big breasted women, lesbianism, threesomes I expect. So why do men want to look at and wank over porn on the internet? I?ve thought about this and so far have come up with the following: it?s immediate, which suits a need for instant gratification, and it?s free. There?s no embarrassment involved in buying it ? unless you?re discovered ? and it is relatively anonymous. It?s also naughtly, slightly dangerous (precisely because you might get caught) and sordid".
That's as far as I got. And then we talked about it. IMHO, anything that you wouldn't like done to you if it was the other way around is unacceptable in a relationship. This I therefore construed as unacceptable behaviour in my case. Hard one (excuse the pun!) to deal with, but I'd tackle (ooops, another accidental one!) him about it and explain how you feel. We talked about it, agreed it was unacceptable and he apologised. Good luck. I think your DH has taken it all one step further and I would be livid! HTH. Good luck.