Need Advice

[Pruned12314]

Recently I became friends with a girl about a month ago. I'll just call her girl #1. I knew her for a little over a year though as back then she became one of my friend's girlfriends, but I didn't talk to her till a month ago. So far I have had an amazing time with girl #1 and she's the most amazing friend I've ever had; she connects with me on a level I've never had before. She's also pretty attractive. So the dude she's dating is close friends with another one of my close girl friends as well (I'll call her girl #2). I found out from girl #2 that he actually told her that he likes her and had sexted her. I don't want to get in relationships and ruin them, but at the same time I want to let girl #1 know whats up. Even though he's my bro, that was obviously wrong for him to do that. I just don't know what's the right thing to do in this situation.