Talk to your GF about it. The best part of living with someone, is you don't have to give them your attention every second you're together. If you need time to spend on your interests, surely she does too?

Try to schedule some guilt free time so each of you can do something you enjoy. Just make sure you respect that schedule that you've agreed to, otherwise you'll find yourself with all the free time in the world and no one to share it with.