If you want to stay married, you have to get proof one way or the other. Check the phone/text records to see if the number of texts/calls lines up to the bill; if there are any missing, he's deleting his contact with OW so you won't catch him. Put a keylogger on his computer if he uses one; it will record all keystrokes. Put a VAR under the seat of his car, velcroed, and check it periodically to see who he talks to when you're not around. Ask a friend to follow him on his day off.