My girlfriend has an issue with my concern about her constantly talking to her ex's and wanting to hangout?

I'm 29 she's 23 which alreadys leaves me a lil weary. Anyways... we been together for 3 months and have an amazing relationship and lots of fun together. My only problem is the fact that she remains best friends with her ex that is part of her closest 5 friends that have always done everything together. I can accept that but the crew is making her feel guilty for not being there with them anymore. She has gone out dancing with them and I went with. Anyways...she has plans to go to a concert with all them and I just heard about it. They're spending the night in a hotel together and I don't agree with it when I know there is still some feelings left behind and her ex was a call after he cheated on her. Also...she has two other guys that she was with and they all keep trying to make plans...without me! One of these guys was an affair they both had while in relationships and the other is indeniably in love with her. Her and these guys constantly text each other randomly throughout the day and night. No matter how much she proves she loves me and is there for me, I still worry and don't agree with it. She feels the need to constantly air out her dirty laundry in conversation whether we're out to dinner or fooling around. She talks about her 400 dollar dinners and 5 star nights from these guys. Makes me feel like ****. I communicate with her about this behaviour but she gets defensive and I end up the bad guy. Nothing gets resolved and I can't take it much longer. I really want to trust her but I don't want to ignore my gut feeling and wait to be screwed over. Some advice would be great because I really like this girl and I trully believe she means no wrong.