Wife in Midlife Crisis.. could use advice..

We've been married for 8 years, and together for 13. We have two children ages 6 and 15. About a year ago my wife started going out with her friends once a week and really enjoyed doing it. I figured it was a good thing and so I was fairly supportive. At first it seemed to improve our relationship. However, as time went on she started to stay out later and later. Her friend that she went out with had an affair. Suddenly she started staying out until 3AM. The more I questioned her about it the later she would stay out. Last week she went out every night for six days in a row. She is a stay at home mom and she says that she doesn't know what she wants anymore. She says she just wants to run. She is tired of being tied to the house. I told her to get a job, but she hasn't made any moves to do it. She isn't sure she wants to work on the marriage because she doesn't know if its what she wants any more. She says she needs time and that I need to back off. She glares at me. If I come near her she tenses up. She refuses to talk to me about what is going on. At all. It's been this awkward silence for the past month. I got her to go to one counseling session, but she has thus far refused to go back. She tells me not to freak out that she is going to stay out all night. It's insane. Obviously I would like her to go back to what she was, but I am not sure that is possible. And if she's cheated? I don't want any part of that noise. I know there is a very good chance that she is cheating on me. I just need to prove it so I can let go. She hides her phone and turned off the tracking so I don't have those options. She is obsessive about covering her tracks. I have no access to her email, facebook, or her browser history. How do I go about finding out if she is cheating? I have worked hard to support her and my family. I make decent money and have carved out a pretty good life for our family. I am shocked that she would throw it away, but it appears that is exactly what she is poised to do. Any advice any of you have would be appreciated. I am not going to sit here for years on end while she "finds herself."

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