Jealousy

My boyfriends friend group is kind of strange. They've all been friends for awhile and he dated a girl in it a few years ago. It wasn't serious but it was off and on for awhile.  They are still friends and they all have group kickbacks were they all get drunk and sleepover. I've been to some and his ex constantly gets naked or half naked and dances around. A lot of the time she will flirt with my boyfriend but she also flirts with every guy there. My boyfriend now brings me to all the "kickbacks" they have but at school she still flirts with him and it makes me uncomfortable. I'm not worried about him at all but it still makes me mad that she flirts with him and he still sees her drunk and half naked all the time. I've told him about it and he understands but there's nothing either of us can do. His friends are not supportive of us either cuz I'm new to the group. She has said negative things about me too. What do I do?