Personally I have always needed space, I think Cerunnir probably is similar.
I need personal time to deliberate, relax, do whatever I would do in my free time (not porn) stuff like CF, reading forums, watching movies or gaming and so on. I have this issue will my gf also whom I live with. 95% of my life is dictated by other people, my deadlines, paying bills, buying presents for birthdays/anniversaries/holidays. It's often so hectic that I will want the remaining 5% to chill out, and if I want some peace and quiet when I relax and I want to be left to my own devices.. well, why shouldn't I?