How have you handled a sibling dating someone you aren't thrilled with?

My brother has a girlfriend that I think does not have his best interests at heart. They met in college, and no he is in his first year of med school, and she is in her last year of college. She wants him to spend all his “free” time texting or calling her, and he is really stressed about doing well in school and keeping her happy.

Would you just listen? Say anything? Offer advice? Have her knocked off?