How can I deal with the stress of being a caregiver for my mom?

My mother has been diagnosed with leukemia for 6 years and I am her sole care giver. Have lived together for 12 years. I work a full time job also. She makes me feel guilty if I have the chance to go anywhere or spend one night away. I would be a better person if I could just get away once in awhile. she doesn't want anyone else here so any outside help seems useless. What in the world am I to do? I have give up on ever having fun and I devote every single bit of time away from work with her. don't get me wrong...I love her with all my heart.