my little brother beats me regularly and my mom just... left

So my younger brother hits me. Like regularly. The reason is literally just that I don't do what he wants. Yesterday was Christmas and he kept hitting me because I wasn't responding to what he said. And my mom was RIGHT THERE in the living room. She saw everything. All she did was look at my brother and go "hey, don't hit your sister" and then just... lay back down.

So I started getting ready to go out. Asked my mom where she was going. She said she was heading to a friend's place to hang out.

I lost it. I was crying, screaming, begging her not to go. Like mom, you KNOW he hits me more when you're not here. Please don't leave. And she looked at me and said "I have my own life too" and called me crazy and walked out the door.

She left. She actually left.

I didn't know she could just... do that. Just leave me there. I miss my dad so much. I just want dad to come home soon. I never thought Christmas would end up being the worst day of the year for me.