This is long but I need advice on my gf's ex gf

Ok so I have a situation and am not really sure if I am reading too much into it or not. I need some advice from a third party who isn't biased by knowing either party, involved or me for that matter. So I have a girlfriend and we have been together for almost a decade. There has never been any kind of infidelity in our relationship and if there is one thing we do have,it's open communication. I am more of the outgoing one and she tends to be a little quieter until you get to know her. This being said I have always had a large group of friends, which have now become her friends as well, but she has never really had many close friends. Recently, her ex from like years ago had reached out to her asking if she was going to this beer festival. She said that we both were going and her ex asked to come. She asked if I cared. I said I didn't desire thinking it may be weird but we all went. Her ex was pretty nice actually and I actually had a nice time. Since then her ex and her have been texting a lot and hanging out - sometimes on their own and I have been there a few times. She always told me one of the many reasons they broke up was that her ex was flirty and she didn't like that. Needless to say I can see where that's coming from. She is very touchy with my girlfriend and even with me. I don't get bothered by much so I could care less about that really especially because it was seemingly just her personality. However things have started getting to the point where I am starting to question what's going on. The one night we were out and we were all drunk and there was loud music playing. In the midst of it she tried to get us to do a 3 way kiss. I awkwardly played it off like I didn't hear her and moved on. Again I figured it was the alcohol. Later in the evening we were all dancing just having fun and I felt someone behind me dancing with me and her hands were in my hips and her fingers were slightly under my shirt and just under the top of my shorts on my bare hips just to the point where it felt uncomfortable if it was anyone but my girlfriend. At first I thought it was my girlfriend as we were all just dancing having fun and then Inrealized it was her ex and my girlfriend was over talking to another friend. I was taken a back and didn't wanna be awkward so I said I had to go to the restroom. Again, thought it was the alcohol and her just having a flirty personality. She also makes comments about how "hot" I look in a kinda joking but kinda serious way. She will say things to my gf too sometimes but again in a kinda playful jokingly way. Tonight she invited my girlfriend to a concert because she had an extra ticket through her work. They went and I was going to pick my girlfriend up whenever she called so she didn't have to drive home as they were drinking. She sent me a text that I didn't see coming and asked if I would mind if she went home with her ex to make sure she got home ok because she said she was really drunk. Neither of them drove and they were going to take an uber back to her house. She assured me that she would sleep on the couch and even asked to make sure I was ok with her staying there. She said she would Uber home if I wasn't. Her ex lives on the other side of the city and I didn't want her to spend all that money ubering home so late and alone when she had been drinking as well. So I told her it was fine. She wants me to pick her up in the morning which I said I would do. Just to add more ridiculousness to this story, her ex is supposedly bi. They dated years ago and she has since been married to a man and is now divorced and supposedly likes some other guy but she has yet to bring him around and is constantly talking to my girlfriend about how she doesn't think he really likes her and he is leading her on. I trust my girlfriend 100 percent but I am not really sure if I am thinking too much into this. Is her ex really just a flirty person and is not trying to cause anyone harm and I m being ridiculous by looking for things that aren't there? Or does she maybe still have feelings for my girlfriend? Or does she likes us both? Like I said my girlfriend said she is really happy she has a good friend in her life now and I don't wanna take that away from her if there is really nothing going on. I also don't wanna accuse or even bring it up because IF there is nothing going on I don't want her to feel awkward around her friend. Also I realize this is long and I could expand more about little things that have happened but I figured this would give the jist. Thank you to anyone who answers. And if I sound nieve, please don't fault me. I have never dealt with a situation like this before and always try and look for he good in people. Thank you and any advice on what to do is appreciated. -Jamie