I relate to your situation, as I am also a CS student working full time, at a web agency, with lots of responsibilities, making shit money. I understand the hesitancy with quitting even with such horrible working conditions. The fear that no one will hire you full time since you're still studying while bills and rent piles up can be overwhelming. But it's clear you know that your boss is taking advantage of you and treating you poorly, so you have two options: take the risk quitting or wait it out until you graduate.

I don't think there's a right or wrong answer. Personally, I've waited it out for the last 3 years, and will be graduating in a few months with a strong resume. I feel I made the right call, but I don't have a horrible boss, just an unreasonable level of expectation for the salary I get and value I add to the company. Unfortunately I can't say much for you except maybe it's time for you to take the risk, especially if it's pushed you as far as to post something like this online.