How do I tell roommates i'm moving out?

I already signed a renewal contract to live with the same 3 girls again next year, but I've decided I want to live somewhere else. These girls are nice but they always stay at the apt all the time and bombard me with questions when i come in from somewhere. They also treat me like I'm 5 yrs old...i'm shy but they act like I'm stupid sometimes. They have to know everything I'm doing all the time, and I feel like I'll have more freedom with somewhere new and make friends and not be dragged down. When I tell them I know they'll be mad drill me about why i'm moving. What should I say to them to keep it short and how should I tell them? Thanks.