Cheating wife....why?

I recently found out my wife has "fallen in love" with a guy she met on her ship in the Navy and has known for like only a few months. She has been having an affair of sorts behind my back. I can't prove if she has done anything with him physically, but their emails back and forth suggest it. Besides, finishing your emails with "I love you baby" is cheating in my eyes. Anyway, we were really happy...planned on family and all that stuff. She went underway for a few months, came back and was totally different. I found out about her "relationship" the hard way. I have been trying to work it out with her for the sake of our marriage but she said she doesn't want to be tied down in a marriage anymore. She wants to be able to go to clubs and grind on random guys, go party and get drunk all the time, etc, etc. We've been married for 4 months. She said that she doesn't know if he may ACTUALLY be Mr. Right and said she wants to find out. What does that even mean? What do I do?