I felt the same way at various points over the past year; as a child I was badly beaten up by my violent step-dad, bullied emotionally and physically every day. I had a few brushes with death during this time, lost my ability to speak when I was 13, for a year, and when referred to a psychologist of sorts at age 15 I was diagnosed with having lost the capability for emotion completely.
I fought through because I wanted so much to get to uni, get an education, and make something of my life, and thankfully I managed and got away.
Since returning for a month over the summer, my Mum's apologised to me for never leaving my Dad in the thousands of times I asked, and has explained to me that he's now treating her like rubbish seeing as I'm gone. Apparently he shows no love to her (I've not heard them talk once without shouting/swearing in the three weeks I've been here), he also forces her to work as his receptionist for his business. She has no qualifications but would love to have a different job, yet he won't let her go out and get a new qualification, claiming that she's not good enough to do anything else and she'd be a waste of money for taking a course. My Mum's told me she hates her life, wants to escape or end it, but my Dad's claimed all of the family's money as his own under his business account, so she has nowhere to go, no money to escape with, and no chance of getting any money as she's not allowed to leave the house.
Obviously, this has put me in a similar position to you in the past, and though university is the first place I've ever felt happy, there was a time during the year that I was on the verge of dropping out and getting a full-time job to pay for a place for my Mum to live.
HOWEVER, I thought harder and realised that although this sounds terrible, I DO have my own life to live, and it's important that I make something of mine, as my Mum never had the chance to, and unless I'm the one to break free, it'll be a cycle which will carry on for a long time; I want to make something better for my own future, and as harsh as it seems, I can't have the family I grew up with holding me back at this stage. Obviously I do love my Mum and care about her, and it hurts me like it does you that she's just 'existing' and not living, but if I try to help out, I'll put myself into that same position.
I know it's difficult, but you need to realise that though family are important, you are your own person and you shouldn't let the decisions and choices of others destroy you, or make you feel guilty - you need to move on somehow in order to avoid being sucked in.