Why does my significant other keep getting into my email?

I swear, I don't leave it signed in. It's like she is monitoring everything I do, like on Facebook, when i add someone new, and it happens to be a women that I either knew from school or grew up with, for the the love of God, what gives? I have nothing to hide, as I have left my email or facebook open before. But this is getting almost creepy and concerning. I already confronted her and she denied it at first then admitted it. Later she said she wouldn't do it again and I just found out that she was in it yesterday. her excuse was that she happened upon my email being signed in. last night I did not even leave it open at all. She is going down the psycho road or something again. Go ahead all you women who have trouble with men, go ahead and flame me. But you need to know what's really going on and our relationship before that. It's not bad , but it can be better. The way we were ever started is rather odd, because it was more by accident so we have just cohabited or domesticated ourselves to each other over the years. Not a good way to start. But our relationship is a lot better than those I know who are married or have started as a mutual couple who chose each other to be with. I am not looking for other women or relationships either, and i know this is something someone will criticize me for, go ahead, I don't care. As I said, this is only part of the picture.