School comes first in my opinion. School is a student's job.
Jobs come and go, but your degree will always be there. You only have 3 semesters left. That isn't long in respect to life.
You shouldn't quit school to work full time just because you're making some money now. Money often clouds judgement. I've known more than a few people who have dropped out of college because they thought they became some big shot making some money. These people ended up screwing up their lives a few years later down the road and regretting they didn't finish school.
I'm not saying you're doing that or have the mind set, but just be careful.
Having a college degree will help when finding other jobs. Most companies would not take on an employee without at least a Bachelors. Or at least in my field (BioSci), most will not hire anybody below a BS degree.
It sounds like your boss is very understanding. Let him know that school is your number one priority until you graduate. I'm sure he would respect that decision. Come up with a compromise. Maybe work full time in the summer if you're not taking summer classes. And work part time during the regular school term. Tell them you can still work for them, but maybe not as much as they want you to until you at least graduate.
It would be such a waste of an education and money if you quite school or fall behind now. You've accomplished so much already, you're almost there to your degree. You just got to push on a little longer! I believe in you Aaron.