Wow! Talk about mixed messages! In your first post you're worries are "I won't ever be able to turn her off". In your second post you say "I love her very much". Why would you want to "turn off" someone you "love very much"?
I'm not doubting what you say are your feelings for your girlfriend but I do feel YOU are doubting your feelings for your girlfriend. Yes, everyone needs their own space and as Little Neo wrote "If you both love each other, you will be sensitive to each other's need for space and time alone." (BTW: nicely said, Little Neo!). I'm guessing though there's more to it here (as many have already noted). Does she do something that annoys you? Is she clingy? Is she an inane chatterer? Does she expect you to spend all your free time with her?
You need to figure out if you just want time alone or if you want time away from her. That's important!