Jess decided that go and live with Luke under the condition that he stay out of trouble and go to school, and he did not do either of these things. The "stability" of his living situation was always taken care of, so the excuse that Jess "needed" to work to support himself is bullshit. He asked Luke to support him and Luke agreed to, but then Jess decided he would rather work than go to school and broke all of his promises to Luke. Again.

Jess wanted to be treated like an adult and be allowed to make his own rules, but if he does that he can't be asked to be supported as well. Luke is under no obligation to support him if Jess refuses to follow any of his rules, and if Jess felt that he needed to work instead of go to school because he didn't trust Luke to support him he shouldn't have asked to come back.

The bottom line is that once Jess has Rory he didn't care about the rest and decided school wasn't worth his attention and he'd rather be paid for his time. Luke even personally offered him money so that he could concentrate on his actual responsibilities, but Jess declined because he didn't feel like it.

He broke his promises and refused to obey Luke's rules. Luke is under no obligation to coddle him under those circumstances.