Hey Samantha. You and I have done a lot of "talking" at this site, both in threads and behind the scenes. My sense is that you are a very strong, talented person with a lot of ambition and passion.
Unfortunately I think a Hell of a lot of us have been with people who just don't edify or inspire us. You aren't alone. Here is the main message I "heard" in what you just wrote:
"I know I need to end this relationship, but I'm scared."
But just for clarity that it's what you really want, I have a question for you: Pretend you're older and you have a daughter who is looking to you for advice. She tells you she's really ambitious and knows that she's missing out on learning about other people because of a r-ship she's in. She tells you she wants to date others instead of living a coupled life of quiet desperation. She's sick of the fights and trying hard to change the guy. She tells you she's basically bored and no longer in love him, although she loves him. Your daughter is upset that he lacks her ambition and that he is content to live his life on the couch; that he has a tenuous r-ship with the truth. Mostly, your daughter tells you she wants to strike out and learn about other people, including dating others ... Would you tell your daughter that she should continue her life with that man? What would you tell her?
If you're worried that you'll be plagued by guilt or will somehow be the villain for leaving him, let me assure you: guilt is something any normal person would feel for ending a long r-ship. That's normal. And you'll work through it, if that's your choice.
As far as you being a villain, think of the r-ship as a business deal: You put 75% of your effort into it while he contributed 25%. No one is a villain, but it's not a good investment for you. You're cheating both of you if you stay in an unhappy partnership. No one (including this guy) deserves to be with someone who is ambivalent about him and wants him to change. That's not fair to either of you. If you need to feel guilt, feel guilt about staying for the wrong reasons. Will he be hurt? We both know the answer to that. But imagine how much more hurt he will be in another year, when you all but hate him and you (still) end up leaving him.
If it helps, and your school has cheap counseling, I'd sign up for a few sessions of that so you have someone there as you do this. Or maybe you just need to get it over with now, by yourself. I have faith that you'll figure this thing out.