If she's your wife it's your business.

Read through any text on facebook to see if there is any suspicious being said.

Start collecting information about her activities online and her cell phone.

QuickSilver can tell you how to install software on your network so you can read what she's communicating each night on the PC

Does she have her own PC?

Stitch please move these questions to your own thread on this forum (create one) and we can expand further and help you out.