My boyfriend constantly lends large amounts of money to his ex, yet he never gets it back?

I don't know that you should confront his ex about it. She may not know that you don't approve, and that could just cause more friction. This is something you need to discuss with your boyfriend, with more than a "look of disapproval." If he is constantly doing something you don't like, you should reevaluate his commitment to you and your relationship.