Decades ago someone told me that the only way she had found to cope with her mother was to understand that what she wanted from her mother, her mother didn't have in her to give. At the time, I didn't understand.
There's even a saying for it: You can't get blood from a stone.
Years later, I'm grateful to my co-worker for her totally unexpected admission. I have found her solution is easier said than done - to stop wanting or expecting something that is never going to happen. Hope you can manage it. I haven't yet, but I'm still working on it.
Please remember to take care of yourself right now. And don't forget to make and keep plans for your future. It will come knocking out of the blue and you need to be ready.
Taking care of you IS your number one job. (Like putting the air mask on yourself first on an airplane.) Taking care of mom needs to take 2nd place.
If you care well for yourself, knowing deep down that you are worthy and deserving -- and you ARE -- you can get by without a loved one's caring about you, even if it never quite stops hurting, even when it surprises you again and again. They are not the center of your life, you are.