Welcome Grace99: I'm sorry you are having a tough time with your sister. It can be very disturbing to deal with someone who is angry and unpredictable. Is your sister getting some form of treatment?
Sounds like your mom is ignoring you.  :)oes your mom have any mental health issues? Have you been able to talk to your mom about the difficulties you are having?
You say your sister pressured you to end your friendship with your best friend and then was the cause of you losing your boyfriend. Could she have been jealous? Perhaps you can try to patch things up with your friend. It wouldn't be optimum, but you could just not discuss your friend with your sister. Perhaps you could meet up at your friend's house?
Have you ever tried to set some
BOUNDARIES in regard to your sister? Boundaries are for you and your sanity. You sister doesn't have to agree with your boundaries and they are up to you to enforce.
I am struggling so hard here and I just don't know what to do any more. I have dropped out of schooling due to all of the days I've missed due to her and I am nervous I am going to lose my job. My health is super bad and I just can't even handle life some days. I feel selfish about wanting to leave them all behind and just leave tonight. I just feel like a complete and utter failure.
Is there anyone else you can stay with (father, other family member, etc.?) What's going on with your health right now? Are you seeing a doctor?
You are not a failure. You can come back from this situation and things can get better.  :)o you have anyone right now that you can talk to? Do you live in the US?
If you live in the US, the resources below could be helpful. They offer help and possible resources to anyone who is in distress and needs a person to talk with (you don't have to be suicidal).
SUICIDE PREVENTIONwww.suicidepreventionlifeline.orgTEXT CRISIS LINEwww.crisistextline.org/how-it-works/You can't change your sister. What you can do is learn to set some boundaries and use some communication skills to help deal with your sister. You can make things better for you by changing the way you interact with your sister and how you react to her.
What are some boundaries you might want to set with your sister? I'm thinking you might want to prevent your sister from interfering with your personal relationships.