About 6 months ago me and my wife separated. We were apart for about a month. Yes, I went out with someone else but I thought that was ok since I didn't think I was cheating. We got back together for the last 3 months. I never mentioned it to her but she found out and wants to separate again. WTF?
As with many couples who have separated for a period of time, the two of you never set ground rules for the separation. Obviously, she had different ideas about what separation means than you did. She may have just wanted time to think, whereas you thought you were apart, so all bets were off. The two of you need a good couples therapist to help you through this if you want your marriage to work.