Should I feel guilty if I want to stop caring for my grandmother and start my own life?

My grandmother has 5 children, 15 grandchildren, good financial resources and her home is that gathering place for our whole family, my cousins come through to stay a few day routinely, some every few weeks, some a few times a year. Two of her children live nearby and visit routinely, and my aunt lives 5 hours away but will come and stay for a week or weekend every few months.
My sister and I have lived with my grandmother on and off for most of our adult life (I am 27,) and the care that my sister and I have provided has given my grandmother a very smooth transitions from independent adult to dependent senior. It has worked well for all of us, my grandmother got loving care and company (her husband, my grandfather, died over 40 years ago, when the kids were very young) and my sister and I had a home base while we were in school, sorting out early relationships, etc. But in the last year I have finished nursing school, and my grandmother's needs have intensified, and her mood has darkened. She is unhappy with all the food brought into the house and cannot/will not understand that she is no longer capable of cooking for herself (she is physically weak from arthritis, and is very forgetful and easily confused.) She complains that she is lonely when no one is visiting and that people are to noisy and disorganized when her family is around, she is insulting to some of my cousins and their spouses, calling them fat and sneering about them behind their backs, these judgments are not out or character, but she is so much less subtle and no longer expresses any regret or caution when she say such mean things. I feel like my love for her is being pushed to the breaking point, I desperately want to move out and start my own life, my sister needs to focus on her new marriage and career, and my mother and aunt are also busy, enjoying post child freedom, starting new jobs and projects. My mother has hired I house keeper to come in two morning a week, and she is working out well, but the implications of this have upset my grandmother, as has my request that my uncle come and cook dinner every sunday. I feel like my grandmother's decline must be due in part to my impending departure, and as I have no marriage planned, do not plan to have children, start a family etc, that it is foolish of me to place my meager life plans (live alone and knit and garden a lot) ahead of maintaing maximum stability for her in the last years of her life.
Aside from arthritis and increasing confusion and memory problems she is in good health, and could live for another decade. I feel like at the end of that time I would be a shell of my self and my life would have passed me by.
I want to be able to go visit my boyfriend with out having to notify my mother/sister. I want to enjoy the dinner I've cooked without someone complaining about it, I want to plant a garden without someone coming along behind me and removing my labels and planting on top of what I have planted, and I want to invite my BF over and have some privacy, without family likely to drop by at any time and without having interrupt our evening at 9pm to check if grandma has taken her meds.
Mostly I just want some time alone, and not have to listen to her litany of worries and complaints (the same every day) after I get home form work. And I want to enjoy her company again, she used to be such a wonderful woman.
What should I do?