Managing classes, part time work, and a relationship

I'm a slightly older student pursuing an engineering degree and I'm entering my sophomore year. I am currently working part time an on campus job (that's not related to engineering). I am about to take calculus based physics, ordinary differential equations, and intro to programming in the fall. I am also in a long term relationship (we live separately -- he lives with friends and I moved back with my parents to go back to school full time since I wasn't getting far financially with my previous jobs).

I can manage financially without this part time job for the school year (I just needed it over the summer) so I am debating if it's best to quit to focus on my classes. Im not the best at math but with lots of time to practice I can do okay.

I'm trying to figure out the best way to manage my time so I do well in school. For those of you out there taking classes while working and managing a relationship what works best for you?