Staying with a girl out of pity?

I've been in a serious relationship for a year and a half. I'm not satisfied with the the relationship, there's lack of sex (usually twice a month) too many fights over the same stuff (we both have a bad temper) she's too clingy and her insecurities drain all my energy, to name a few.
She has absolutley zero Friends. Her mother texts her only when she needs something (usually once every 2 months or so) and her sister never ever calls or writes. She depends on me for entertainment, love and companionship. It makes me feel trapped. Im moving away 2 hours feom her for university and she's devastated, but i feel i have to do this to get some space, to breathe. I dont want to leave her because i do love her, i dont want her to be all alone in this world. She is a hard person to be with though, sometimes she gets very mean and obnoxious without any reason at all, i kinda know why she can't keep friends. She screams at her mother and always wants to be right. Not the most pleasing person to be with. But i still love her and she doesn't deserve to be all alone, if we break up she'll have no one to even tell we've broken up. Its extemley sad. I want to live my 20s with more freedom than this, but i dont want her to suffer. What should i do?
Staying with a girl out of pity?
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