I guess I just want someone to talk to who can understand. 

My Mum's boyfriend is emotionally abusive. He has OCD and is likely on the autisitc spectrum but nobody has ever made me feel so completely and utterly destroyed like this. I made a simple mistake such as not getting in the shower quick enough after starting the running water (he literally timed me from when I turned the water on and when he heard me getting in, it was 1min40secs in case you were wondering how henious the crime was) and he was so horrible to me. He turned the water off, shouted at me to come out and began shouting at me aggressively, swearing, being very intimidating. This is common if someone forgets one of his 'rules'. I really struggle with being shouted at, it affects me a lot and he is aware of this. Later on, my Mum approached him and aasked him not to shout at me like that, and shit hit the fan. He started shouting at her (he is literally terrifying when he shouts) claiming I was ruining everything, insinuating that she didn't raise me well, that I had no respect and so on. He then stormed upstairs shouting my name, my brother hid me in his room and stoof in front of me. He told me to pack a bag and get the f*ck out, over and over again. 

I made a mistake, I apologised profusely, offered him money for the 'wasted water' but he wouldn't listen. I said I was so so so sorry over and over again but nothing works. This is one example of many other similar occurances. My Mum says that she can't leave him because she would effectively be financially destitute (we live in his house) and she won't leave him because she wants to fiancially help my twin brother and I through university. 

My Mum is the most amazing person and deserves better, but I don't want to make things harder for her by telling her to leave, she already feels terrible about the way living here makes me feel. 

Thankfully, I'll be leaving to go to university soon so I won't have to be around this awful man, but I know I'll have to come back- and I don't know what to tell my Mum. If he kicks me out my Mum will most likely leave him, but then it would all be my fault. I just want to talk to someone who can relate or offer me any kind of advice, I feel so defeated.