My friend's boyfriend isn't treating her very well. Is there anything I could/ should do?

I know, I know, relationship question, ugh. But one of my best friends has been dating this guy for a while, and everyone notices that more often then not he doesn’t treat her very well anymore. Any time she wants to do something without him he gets all mad, says “fine then.”, and storms off. When she goes to talk to him about it she comes back completely agreeing with him saying he’s just in a bad mood. This happens almost daily now. The more time they spend together the less she notices that he’s not treating her or anyone else very well. They’ve broken up and gotten back together twice before this because of something he did, and it just doesn’t seem healthy anymore. Is there anything I could/should do about this?