What should I do ? I'm scared and confused.?

Okay well to start off I'm a 15 year old girl. That's dealing with more than the typical teenager. So of course family is an issue. My father has abandoned my mother, brother and Me. Recently my brother and mother have been fighting due to my brother being so infatuated with his girlfriend. So my mother has been coming to me of what to do, and i've just been trying to help. Well she was angry on friday night and took it out on me so me and her kinda had a little episode and she got up and left then finally came home this morning. Her boyfriend was here left to watch over the house and my brother and I. Tom, my moms boyfriend is basically my father, although the past several months hes been kinda freaking me out. Like went in for a hug before bed, he grabbed my just little things like that. Which made me very uncomfortable.. I kinda ignored it because hes been drunk, although i know its not a reason but.. i just don't know. Anyways last night. he came home and it was just me and him in my house. He really made me uncomfortable with the things he was saying to me. Like "lets go upstairs and cuddle watching tv" He is a 47 year old man and it's really freaked me out. I honestly don't believe he would do anything to me, but it has me very scared. He also was saying Come sleep in my bed and i replied saying no, I'm staying up tonight, not going to bed. Well when my mother came home i was scared to tell her because she's been too stressed with other things. But i had to tell her, So i did and she is just shocked.. And i'm scared because If tom leaves.. We will have nothing.. He pays for this house, my moms car, Just almost everything cause my mother doesn't have a job because Tom wouldn't allow her. So he basically has my family wrapped around his little finger and I'm scared, and uncomfortable in my own house. What should i do. I need major help.