Preparing to Leave...

Hi,
I'm 26 years old and still living with my parents. My brother is 34 and he too, still lives at home. Neither of us have ever lived elsewhere. We both work full-time and pay board and pull our weight around the home. We have always had a very close knit family and whilst I always thought this was lovely (and of course part of me still feels like this), and I know I am really very priveleged to have this kind of relationship with my family, I am starting to feel almost, well, resentful of it. I look forward to starting a life of my own, in my own place etc. but really feel quite immobilised by the guilt of "leaving" my mother. I know this isn't healthy, and I know if my mother knew I felt this way she would be mortified, but I know she will really struggle with this. We have talked about it, and I know she knows the time will come one day, but even booking a 1 month holiday in September abroad has been enough to send her into depression. My parents have always had control over things -i.e where we were, what time we'd be home etc. Always - even now that we are much older, but I wonder - I know there are others out there that have gone though this and gotten through, and I just wanted some advice on how I can support my mother through this and overcome my guilt? Any thoughts would be appreciated. Thanks!
Carly.