I've been through this as well and it is horrible. You need to talk to someone about what is going on at the moment, it's easy to feel like it all has to be about your sister right now but you need support too. Ideally talk to your parents/family but if you can't, talk to someone at school. Try and look after yourself and do some nice things and self care. There's not really anything I can say to make you stop feeling the way you do, seeing your sibling in such a scary state is traumatic and the constant worry about what they might do next is horrendous... just try and find some support to get through it.