You both lived with eachother for over 7 yrs. Why have you both just lived with eachother. Were you both not ready to take the next step towards marriage. I know some women can be fickle about things like that. Maybe her leaving is a way to un jar your emotions and to get you to realize that she is the one for you.
I know I went through something like this. I was with my boyfriend for 8 yrs and 2 children later. I was looking for the commitment and didn't recieve it. I told him I got tired of waiting and I left him. 1 month later he told me that he could not live with out me in his life and he purposed to me. But then again...I don't know if this is the situation that you are in.
It could be a number of things. Please give more detail so as I can help you more. Thank you