Just wanted to say how sorry I am that you found all that on your computer Agonycat BUT it is good that you found out now.
I didnt find out about my husband's online chit chat/flirting until after he had gone to meet THEM at a party in another city in the US! When I saw EVERYTHING I immedately emailed them and told them I found it all and his bags would be packed when he got back. Ruined his weekend anyway and nothing happened. They actually turned out to be not all that they portrayed online! Surprise! He looked like a wreck when he got back... early!
We had been together for 18 years by then! He moved out but we saw each other all the time because of the boys. We talked and talked and after 8 months decided to try and make a go of it again.... 2 years later all is well! I dont worry about him on the computer anymore.... he has learnt his lesson and grown up a bit {He's 43!} As a safeguard when he moved back in we deleted ICQ and changed our email address.
Its good that you saw it now.... you can catch your husband before it gets any further. In my opinion, it just might?? I agree with Nat... online or face to face, its cheating.
Once again... I am very sorry and the best of luck to you. It's NOT your fault.

Akiwican