When being primary caregiver for aging parent with worsening mobility issue, how to not be abused by them and losing self?

Overwhelmed: If i understand your question, you feel overwhelmed physically and mentally. Your health is just as important and you of course can't take care of your parent if your health deteriorates. Try to get nursing help for the parent if they qualify, try to get other family to help, talk to friends and if needed, psychologist/psychiatrist. It can be overwhelming, dont do it alone.