Weekend Events

i'm hoping that someone could give me some help on this little problem i'm having. i'm in a sorority, and at the beginning of school every year we have a lot of parties every weekend for awhile. ok, to be honest a lot of drinking goes on and i do take part in it although i do try to be careful(no drinking and driving, and watching out for my sisters. and i ALWAYS make sure that i never drink in my letters b/c i respect my sorority and my sisters too much to do that. well, the problem is that i'm underage, and if my parents knew i was drinking they would freak out(like taking my license and ripping it up, and grounding me for the rest of my life which they have no right to do cuz i'm 19...but that's beside the point b/c i live at home and commute to school.)i try to spend the night somewhere else so my parents don't know what's going on but most of my highschool friends don't live close to me anymore b/c they went away to college. and when i ask my sisters if i can spend the night at the sorority house they always welcome me, but i feel so bad asking them to do that like evry weekend. i don't want to become a pest to them. if anyone has been in a situation like this before i would love to hear how you handled it. i know i could just sacrifice the drinking to make things a whole lot easier, but when most of the party is participating in drinking games it's not much fun to just sit and watch. i would love any advice on this. thanks so much.