hartbroken,

I agree with determining exactly what kind of space you need before bringing it up to your gf. Being vague with a simple remark like "needing more space" is very likely to put her and you into a tailspin.

Maybe you need a day or two alone per week, or a pattern of days from 10-3 you've got space. Whatever ~ come up with a plan that you really need and then you can approach your gf about the issue.

Best wishes to you and your gf!