Try not to worry about feeling "guilty" because you're parents are around ... everyone has a different relationship with their parents, and so you have every right to be feeling the way you do towards them.
I know I often feel that way when i try and rationally think about my situation with my parents (mom especially), and the only way i can try and not focus on the guilt aspect of it (my parents physically being around) is by reminding myself that i do have the right to feel this way .. its just how you decide to deal with your relationship that matters. (Unfortunately thats the hard part!)
I hope it works out for you ...