My girlfriend isn't who I thought she was?

So my girlfriend and I have been together for a year and a half. I love her, I do, but the longer we're together the more I find out that the things she said we had in common we actually don't. She lied about our favourite types of music, films and other basic interests you have with someone when you get to know them. I'm starting to realise that were not actually a good fit for each other and I'm starting to have thoughts of breaking up. I've never broken up with someone before and the more I think about doing it the more I feel like an asshole. I don't know what to do because I know she depends on me and is way more into me than I her. I need some advice on what I should do be it giving it more time or just pulling the plug. Anyone with experience in this please share your thoughts! Thank you in advance.
My girlfriend isn't who I thought she was?
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