He doesn't think it's fair that he contributes 3x as much to our shared bills (I still pay my own bills) when he makes 3x as much as I do

You aren't married. He justifiably thinks its unfair you aren't paying your share of the bills.

I also can't spend any money on myself without him guilt tripping me for it, saying he's essentially paying for it since I'm not contributing equally to our shared house bills.

He's absolutely correct. If you're blowing money on luxuries for yourself, that could have been used to pay your share of the bills.

I would never be able to contribute equally, because he has 6 years of experience on me, graduated college without any debt (thanks to his parents), and was left 10k from his grandma. I wasn't left shit, had to take out loans, of which I've paid off 18k and I still have 22k to go. Where is the fairness in that?

Life isn't fair. You aren't entitled to money from his parents or grandma. And your defeatist attitude about your earning potential is precisely why he shouldn't be paying your bills for you. If you already think you'll never increase your earnings, then how is him subsidizing you going to help with your lack of motivation?

All he does is belittle me. Nothing I do is ever good enough. He wants to control everything I do.

Thats not acceptable, and you need to put a stop to that shit asap.

I often wish we would just break up and that I could get my own place to prove that I don't need him.

If you can afford your own apartment, you can afford half of a shared one. You'd really just be proving him right here -- that you were using him all along when you could have supported yourself.