Sex , Lies and Videotape??

When meeting my boyfriend, I knew he was quite the perv, as I can be at times. However, what I did not know is that he would continue his conquests online. And how did I find out this information? He left a website page logged onto my computer. I found it accidentally when I went to view the page (we both belong to this particular forum).
I'm pissed beyond reason. I have no idea what I should do. I did tell him about finding it but I didn't go into details. No clue what to do.

Is cyber sex considered cheating?