I started doing a little bit of this kind of stuff when my 15-year marriage was on the rocks. Specifically when our sex life was down to maybe once a month. For me it was a symptom of our problems, not the cause. My W was still very upset to learn about it--and the chatting was much worse than the pictures, in her opinion.
On the other hand, my current SO says she wouldn't care at all if I had a magazine laying around, as long as I came to her for the real stuff. But again, chatting online with some W would be considered cheating.
So, if you want to save your M, my advice would be to spend ZERO time on the computer unless your wife is in the same room where she can see the screen. Better yet, turn it off altogether, along with the TV. Spend time with her. Go on walks together. Admit your mistake, apologize, and consider counseling if you can't do these things.
