What's goin on???

For the past 3 months my roommate and his girlfriend have been sharing a car. Particularly in the last couple of days, i come home, excited to see that my roommate's car isn't home and figure i have the luxury of having a spacious apartment to myself. So throughout the rest of the evening, i claim territory in pretty much every room. i'm chatting on the computer, i put a movie on, and later play and sing a song i've been writing on the piano. while i'm singing of course, i take liberty of my apt's awesome acoustics, only to find out that my roommate is upstairs in his bedroom sleeping. i had no idea. i apologized even though he really didn't seem to care. a couple of mornings later, i awoke on a saturday and saw once again that his car was gone. i was like "sweet! a saturday to myself." so i get up, crank up the news, turn the radio on in my room, even played my demo for a while. i think it was around 2:00pm when i had heard someone get in the shower. it was his girlfriend. apparently she has been working the "all nighter" shifts and sleeps more during the day. again, i felt kinda dumb and embarrassed. now i'm just so confused!! i'm always trying to be quiet all the time now cuz i don't wanna wake anyone up. but i don't even know if there's even anyone here!! and i'm suddenly artistically constricted...lol it's not musician friendly at the moment.
*sigh* i need to learn how not to care bout what people think and just do whatever and not care about it..i'm so worried that i'm not gonna be a good roommate.