I've kind of been taken on a wild ride this past year, and now that the dust has more or less settled, I would like some advice. Sorry if this is long, I don't really have anyone to talk to about this.

I've (21F) been dating my boyfriend (21M) for over 3.5 years now and I really love him. Around last year, our relationship was declining because of my poor mental health and not being a good partner. We both kind of saw the writing on the walls, but neither did anything about it. He had always expressed regret about how things ended with one of his exes (21M) throughout our relationship, and one day he noticed said ex had reached out to him (it was innocuous, a meme or something). He told me about this, and I encouraged him to send something, maybe apologize and clear things up so he could move on with a clearer conscious. My boyfriend and I had talked about poly/open relationships in the past, and I expressed that I was open to them. As the two of them continued to talk more, they realized they still had romantic feelings for one another. Before anything further happened, my boyfriend talked to me about it and I agreed that I would be willing to try it out (I know now that "trying it out" is not really possible with poly dynamics). During this period, our communication was not transparent. I knew they were talking, and knew myself that there was more, but I didn't want to know about it, and my boyfriend didn't really tell me much either. Over the course of 2-3 months they started sexting, and eventually met up in person to do you know what (among other things, I assume). I will mention that he did give me a few days/a week notice that he was going to meet my metamour irl before it happened.

This dynamic went on until around January when I decided I couldn't really deal with it anymore and broke up with him. That lasted for around a week, and we agreed to keep our relationship going until the end of the semester because it would have been near impossible for either of us to deal with while maintaining a good standing in school (and of course we still loved each other). During this time my boyfriend started talking less with his partner, and the two of us were getting closer with one another again. After the semester had ended, my boyfriend decided to break up with his partner, and mostly cut off contact with him. This period of my life was the happiest I had been in years. I now had a stable relationship with my boyfriend, I was also getting treatment for mental health issues, and generally things in my life were going very well.

However, my boyfriend cut his relationship off with his partner quite abruptly and his partner wanted to meet in person to talk. After their talk my boyfriend felt more comfortable around him, like a lot of his issues with him had disappeared, and wanted to keep his partner in his life in some form. So I decided to reach out to him and talk to him. He was very nice, and we started talking more. Later, the three of us met in person, and started doing recreational activities as a group online as well. My metamour and I both realized that we didn't want to date one another, but my partner expressed to us both that he loves us equally and wants to pursue a hinge style relationship, but this time a more ethical version with transparency, and mutual respect between metamours. I agreed to the relationship, but I haven't internally committed to this dynamic since I don't think it would be something I would choose. I have been open about these issues and reservations with my boyfriend, and have been trying to see if I could adapt to the relationship and be happy within it.

Recently I've been really depressed, as a result of everything. I don't have any issues with my metamour, and I don't think the relationship is being carried out in an unfair/unethical way. There isn't any heirarchy, time is distributed quite evenly, communication is open and things are as transparent as they could be. That being said, I feel like this amount of affection and time is unsustainable for me. My partner and I have discussed the possibility of me seeing other people, and even though he would encourage me to do so, I'm not sure if that's what I want for myself. I have also noticed that my partner seems to be changing. It's only been around a month, so it's just things like sense of humour and mannerisms, but it feels like, as time goes on, spending time around a person that important is bound to bring about more change of some sort. I just kind of feel left behind as a result. Most of the recreational time I can spend with him he would like to include my metamour, which I'm not sure if I want to do. I am starting to realize that this person is going to be a massive part of his life (equivalent to my own place in it) and I'm not sure if this is something I want. Preferably I would want a monogamous relationship after thinking about the different dynamics, and so it feels like it would be hard for me to be happy in this relationship. Nevermind the long-term practical complications that come with polyamorous relationships like nesting partners, marriage, living situations, etc. The thing is that I really love my boyfriend. He's comsistently been one of the only people in my life who was there for me, and who really cares about me. I know I've aired out a long list of reasons why I might be incompatible with him, but I genuinely love him so much and it's really hard to express that.

That pretty much sums it up. Thank you to whoever responds and decides to provide their opinion/advice, I will do my best to be active in the thread in turn. Thank you for reading and I hope you have a good day wherever you are.