Kristen thinks that her husband is cheating on her because he has been acting suspicious. He told her to not answer any unknown phone calls out of no where. He claimed he was getting weird phone calls and that they were trying to hack into their lives. She isn't buying that excuse. He even told her to not accept random Facebook requests from strangers. It sounds like he doesn't want her to communicate with anyone who he is cheating on her with.
A long time ago she busted him cheating, so she is a little worried about his recent behavior.