Set your boundaries w/ him . Maybe you can get your parents to go to al-anon w/you to better help them set their own boundaries. Addiction really is a family disease. The addict that makes us hurt and react in ways maybe we wouldn't and through the yrs. the rest of the family may have habitual maladaptive behav. too.
It helps to be communicative our feelings + needs. Let your parents know how it is affecting you and your ability to fulfil your dream of being a good college student.
With addiction in a family often a lot get swept under the rug w/o being talkied about.
let it begin with you. It is your bro's life don't be less than you are capable of bec of his choices. Keep returning here for info and support.