undercoverwife... have you confronted him about this? I would start there. Most cheaters like the thrill of being sneaky, gather evidence so he cannot refute your claims.
I think I saw somewhere that you can download a program that will record keystrokes and input that info into another program so you can read what he's been typing. If interested, google it.
I know how bad it sucks to be going through this, we've all been there.
Hurtin: 32 WAW: 30 D: 8 Bomb: 10/05 Sep: 12/05 Back together 8/07 Bomb (OM): 11/07 Filed for D (me): 12/07