@Idoxide,
Find a roommate and other ways to cut expenses so you can cut back on your hours at work. This also gets your ex off your back.
"Gee, Dave, I would love to help you, but Susan now lives here and I can't just kick her out, you know. "
Practice saying that with the right names, a thousand times if you have to.
As for a place to find a roommate, try your school. There's often someone who wants to get out of a bad living situation and it's some odd time of the year. If that doesn't work, then ask the local market and home repair places if you can put up a flyer to advertise for a roommate.
I don't recommend asking at work but it can be a last resort if you need it. But try these other places first.
Talk to your professors about developing better and more effective/efficient study habits. There may be ways for you to get the work done without it taking forever, thereby freeing up some of your time. Explain you are working part time to try and make ends meet and you really want to make this work and succeed in school. Many educators will be more than happy to help you, and then they will know your circumstances.
You can do this.