My (33m) gf (33f) of a year has just got back from a hiking trip with some friends (2 x m late 30s) and I'm looking for some advice.

We have lived pretty different lives with me being on the corporate / work side and her more of a free living vibe. This more open side of life has always intrigued and I'm a relatively open person in general. She is awesome and I love her. It sparked really quickly and has stuck solid as a rock for a year with very little in the way of real issues that we haven't been able to deal with.

She has come from a background of a little polyamory and her friend group is relatively alternative. I'm more straight laced but certainly wouldn't call myself a prude but I have struggled with some aspects of it. The main sticking point is that she has slept with a couple of people (over a 10 odd year period) in the wider community. This obviously makes me a bit uneasy, but we have talked about it a number of times and feel we have reached a point of mutual understanding. Around how and when we should approach this and act around people.

I have put a few clear boundaries in place and she has stopped seeing some friends as a result of this unease.

So, cut to this weekend. She was going to head out for a hike with some female friends, who changed plans about 2 weeks ago to not travel to the mid point for a variety of reasons. In leu of this she was still keen to go hike and I was already busy with plans as I thought she'd be away. She ended up going with two male friends, both of who I have met before briefly and neither of whom she has any attraction to. She has slept with one of them when she was single and way before we knew each other.

She got back last night and I was not in a good way having been pretty anxious about the whole thing. One of our key ways of looking at things is to spin it 180. Would you be happy knowing the other person did something with someone of the opposite sex and you walked in on it. That sets a relatively clear line between us. She has said she had a cuddle with one friend as they chatted which I was uneasy about, but could get over, I think. But one of my big things is her being naked around others. For me it's just a no. It's different if I'm there and there is a sauna or something with a larger group, hell, even a bigger mixed group of people I wouldn't have an issue, but this was a hard line I had made clear that I wasn't comfortable with her being naked around other guys unless something above was happening.

Well it transpires she went skinny dipping with the two guys on the way out from the hike. Breaking that key rule. She has said she thought about it but didn't think it would be a huge issue as we are pretty stable now and its not seen as a big thing to be naked with a lot of the people in the friend group. It wasn't done in a sexual way at all. Just a plunge at the end of the hike. My stance is that she has broken the trust I have in her, knowing how I feel about things like this and her stance is that it's not seen as taboo amoung her friends so what's the big issue.

Am I over reacting? What approach would people take to this? Am I being too controlling?

Sorry this has been a bit of a ramble, but I want to check im not going crazy here.