I 29 M and GF F29 recently ended our 4 year relationship. Looking for opinions/perspective.

I 29 M and my girlfriend 29F recently ended our 4 year relationship. As I have been dissecting our relationship in my head, I keep thinking about certain events or conversations that bothered me and may have lead to resentment building in the relationship. I’m looking for perspective or opinions on a certain event that occurred while on a vacation together. This trip was only a few months before we broke up, so things were already slightly rocky. We never argued much, it was more that we fed off each other’s anxiety which would lead to our spiraling and irritation with each other for getting triggered, and we had many triggers. During the last day of the trip, we met a family that was very cool and fun to hang out with so we spent most of the evening with them. We had some drinks and there was mention of going to a dance club nearby so we tagged along. My girlfriend and I were pretty drunk, but I was still coherent enough to remember all the events vividly. When we got to the club we started hanging with this same family and some other people, including a random guy that seemed to be there alone. He definitely gave off bisexual vibes and during the night I had seen him dancing with both men and women. When we started dancing, it was me dancing with my girlfriend. Shortly after, one of the female members of the family we had been hanging out with (important information, it came up in conversation that she was gay) came over to dance with us. After some time, she and my girlfriend started dancing together which turned into my girlfriend grinding on her for a decent amount of time. She left to get another drink so my girlfriend started dancing/grinding with me again. The girl came back quickly and my gf started grinding on her again. It was pretty intense to the point where this girl kept looking at me and mouthing “is this okay?” I didn’t necessarily love it in the moment, but I’m not a vibe killer so I just let it happen. It got to the point where this girl told my girlfriend to dance with me again because she felt bad. We danced together for a few more minutes, then the guy I mentioned before ended up near us. My girlfriend ended up dancing near him and then began grinding on him as well. It was short, but the guy looked very excited and seemed to enjoy it a lot. I had an awful feeling watching it happen and almost felt disgusted. I tried to suppress it and kept dancing with her until we decided to leave. For some context, we had danced together before, and she never danced like that with me or anyone else because she always said she did not like dancing like that in public. I didn’t mention anything that night because I wanted some time to pass to process what I was feeling. The next morning, I woke up very early with a pit in my stomach. When she woke up and we started getting ready to leave, she noticed something was off so I told her how I felt. Her first response was “I was drunk” and that she assumed the guy was gay and “one of the girls.” She said she was just letting loose and having fun. I tried to make my point that even if that was the case, to go from saying she never wanted to dance like that to spending the majority of the night dancing like that with strangers did not sit very well. I also pointed out how it felt to watch another guy, regardless of sexuality, obviously enjoy her grinding on him. She did apologize and validated my feelings in that a boundary had been crossed, but I honestly felt like it’s something that should’ve never happened. This wasn’t the exact reason our relationship ended, but I think it contributed in some way as it kept replaying in my head in the following months and always left me with a terrible feeling of being betrayed. I’m not sure if this is overreacting or if it’s jealousy in some way, I’m just looking for some other people’s input as this was my first serious relationship and I’m trying to process what went wrong and why I feel the way I feel. Thanks!