I'm really sorry for what you're going through. Your wife is lying through her teeth. Believe me. If you want to know what she's hiding on her computer, do the following:
Does she have a password to log into her computer? If not and you have access to it when she's not there, then you can install a program that sends you emails about all the activities your wife is up to. The software I used which works amazingly well is called PC Pandora. It's $70.00 (down-loadable) but I was able to find out everything. Just make sure you watch the how-to vids for setting it up and practice (there is a demo version) on your own machine.
