my sibling beats me regularly and my mom left me alone with them on christmas

So my younger sibling hits me. Like regularly. The reason is literally just... if they don't like me at that moment, they hit me. That's it. That's the whole reason.

And yesterday was Christmas. They kept hitting me because I didn't answer them fast enough. I didn't respond to something they said, and they just. kept. hitting me.

My mom was RIGHT THERE in the living room. She heard everything. She knew. And what did she do? She went "hey [sibling's name], don't hit your sister" once. Once. And then she just laid back down.

Then I saw her doing her makeup. I asked where she was going and she told me she was going to sleep over at a friend's place. I completely lost it. I was crying, screaming, begging her not to go. I told her I was scared. I told her if she's here and this is already happening, it's going to be SO MUCH WORSE the second she leaves. Please don't go. Please.

And she looked at me and said "I have my own life too."

Then she called me a crazy bitch and walked out.

I didn't think my mom would abandon me too. I miss my dad. I just want my dad to come home. Please come home soon.

I never thought Christmas would become the day I hate most.