What should I do about my older sister?

I will admit I complain a lot in my life. I'm 28 and I still live with my parents and take care of them, my dad isn't as healthy as he used to be and my mom is going blind. dealing with my mother going blind is not easy at all as i still love her very much. anyways I got into a nasty fight with my sister. I dont have any firends because I have poor social skills (im not a rude person in general) and I have trouble expressng myself to point out the real situation. So she is the only person I have to talk to, and yes I complain a lot and I understand her attituide while doing so, the fact she deals with her problems a lot better than I do with mine. But there were times she was bitchy and pushy espeacially when I needed help, advice or emotional support and in time of need she would be the opposite of nice, her level of ignorance would make me feel small. But I always knew when she needed help or advice I would be on the spot to help right away. I don't know the reason of my complaints is because she is'nt really listening at all, i'm not sure if that's the case. There were times she would verbally abuse me and bully me, she even said I should go kill myself. I wanted to end my relationship with her for many years but due to my parents I still vulnerable talk to her. So I messaged her and told her that im her little sister and you dont have to be a jerk like that, when our parents won't be in this world I won't keep the relationship between us anymore. It pissed her off and she said she will call up our dad and tell him how I complain and what I said to her. Naturally i felt hurt and embaressed i feel that out of all the mean things she says im not allowed to say anything back at all, its simply what I thought. She lives with her kids and husband and I live with my parents. What should I do or say if she decides to embarasse me infront of my dad or mom and how should I talk to her forward on?
What should I do about my older sister?
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