We've been dating since march and at the beginning it was only meant to be a casual and non exclusive thing. We both expressed interest in an open relationship too. We agreed we could date outside of our relationship but it appeared that neither of us had acted on it. At some point the dynamic changed and has been slowly morphing into a committed open relationship without us really talking about it. We just spent increasing amounts of time together, opened up more, shared more, etc.

Last week she met a couple for a threesome, she gave me the heads up beforehand and even asked me if I'm still ok with it. We talked through it afterwards and about our needs etc and it seems fine with me. We're still figuring out exactly how to do this but I felt like we did it, our first open relationship experience.

Last night she told me that a friend she meets about once per month, (since before we began dating), isn't just a friend but they also have sex. I mean, I'm not really surprised. She goes to his place to smoke up together and he runs some sort of erotic play thing too, so it's hardly the shock of the century but being told sooner would have been nice.

At the start I presumed she was sleeping with him but we didn't have the sort of relationship where we'd be expected to disclose that. I also just wanted to respect her privacy and not overstep as I enjoyed spending time with her. Later on, since she always just referred to him as a friend I believed that's all it was. I don't know, after a few months I didn't want to ask either as it might seem like I don't trust her and I really believed she would have told me. Especially since she asked me about the threesome.

In any case I feel quite hurt by this one, but at the same time I don't really blame her. I don't think there was a clear point this turned from a casual thing where we had no expectations to disclose that stuff into a more committed relationship. So I'm upset but I'm not really mad at her and don't really blame her. She could have done better, and I laid out my expectations for the future. She apologised a lot too.

Even knowing all this, I'm still pretty upset about it. I'm not sure what can really be done tho other than laying out the ground rules for the future. I'm considering asking to chill on the additional partners for a while as our relationship is going through a lot of changes at the moment. We're talking about being serious and potentially having a future and I think it's just a lot of new things all at once.