Wait. Your brother is saying that he drives around for hours because he feels awkward and out of place at his brother's home? Who is paying for those hours' worth of gasoline? If he put those driving hours in at a job instead - any job - he could still be away from his brother and start to be self-supporting at the same time.
So don't worry about saying no to the boy if you have responsibilities and he wants you to shove those aside and focus on him instead.
If he does come to your house, put him to work! Have him fold the laundry, do the dishes, clean the bathrooms, and tidy up the house so you can study. Tell him he must be quiet while you work, and he must leave at 10 p.m. Offer to give him a book (maybe a motivational book?) to take home with him if he has nothing to do where he lives. If he must spend his free time at your house, have him use that time to your benefit. You're a homemaker, a student, and a mother. You have time to be a sister to him, but not a babysitter.
P.S. I just read your "So What Happened?" comment. I'm very glad he has two jobs! I'm glad he's doing so well that he received a promotion.
If I were living with a brother and that brother was (as he might indeed be doing) bugging me about why I'm not saving any of the money I'm earning, I would want to stay away from him, too. But this boy needs to take a look at himself and figure out why money is slipping through his fingers. There could be a lot of reasons.
He can still help you when he comes over. And you can still give him a good motivational book to read. Maybe it will motivate him to find out how to handle his paycheck, without any naggin' ol' siblings telling him what to do! :^)