Has your wife ever lied to you before??? If not try to get past it. My wife got her own e-mail account shortly after she desided to leave. It killed me at first but I now realize that she is trying to start her own life and if I have any chance of getting her back, she will always have her "own" life. It is something I wish I had realized years ago.
Does she have your email account name and password? My wife does and I'm fine with it. I always thought that my wife and I would share everything and everything that either of us wanted the other would. It ended up that whatever i wanted was ususally what we got. Giver her the time and space she wants and if she does have an e-mail acount so what. Trust is another thing you have to have other then giving the time and space.
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Find more sites and reading material on this, it will help even though it is driving you crazy.