Unnegotiated boundaries

After a boundary miscommunication, what happens when you can't seem to let go of that feeling of betrayal?

I have been in a relationship with my partner for a few months. I’m monogamous as far as I know. When we started dating after knowing each other for a little while, they had newly discovered they were polyamorous (non-hierarchical) and I went into things feeling comfortable, knowing the overall gist of what it would entail and accepting the different challenges that would arise.
About a month into our relationship, they went on a date with a new person and although I was nervous, we both agreed that they would take things slow in order to give me time to adapt to the change. Also, they had mentioned to the new person that they were already in two committed relationships, and therefore did not have time for a third one that was as time-consuming as both of the ongoing ones. Only a few days later, them and this person began dating, and it came as a complete shock, especially because I had explicitly set a boundary that they had disregarded.
Since then, we have talked about it a lot, and they have sincerely apologized for their behaviour as well as put in a lot of work to make me feel secure and loved in our relationship. They also explained that, to her, saying they're "dating someone" is only another word for being clear that they are both interested in each other and want to continue seeing each other in a romantic capacity, when I had imagined their relationship to have taken on as much importance as ours within only a couple days.
Overall, this particular aspect of things was a misunderstanding of terminology, but this only was clarified several weeks after the event itself, so I still spent a pretty long time feeling quite insecure and on edge before finding that out. They did still apologize for having been inconsiderate and for having broken my trust despite not having seen it that way at the time. To be honest, we have both made a really considerable effort to make things right and to rebuild the trust that was broken, and our ability to work through the feelings that have arisen has also been really good in most respects.
However, even now, several months later, I can't help but feel as though their relationship is happening at my expense. As a result of what happened, I've been really on edge, anxious, I'm experiencing a lot of paranoia. Because of it, I think them being together is still a bit of a kick in the face for me. This is also because the relationship between my partner and the (not so) new partner in question has become a lot more serious and time consuming than anyone had originally anticipated. This has definitely contributed to a bit of a feeling of competition between members of the polycule for the time we can spend with our mutual partner. We all like each other and get along fine, but time management, in addition to the other stuff I’ve mentioned has made things between us a little fraught in that sense.
My partner has been very clear that their other relationships do not affect the way they feel about me, that they are just as committed as they've always been, and they have definitely made a huge effort to preserve the sense of consistency I've been needing and to make sure my needs are met. I understand that it is a new thing for them to see multiple people at once, and that they are bound to make mistakes, but I also want to advocate for myself.
I’m having trouble finding a solution here that makes it possible for me to be comfortable and secure and address the ways in which their other relationships are affecting ours with regards to time management and the ability to be present, while also forgiving them and moving past the mistake they made and has since been working very hard to make right.
I'm also aware that I have a lot of underlying issues that have contributed to the response I'm having (GAD, BPD, trust/abandonment issues, some pretty low self-esteem, the whole nine yards), so I think that constitutes another big motivator to stay in this relationship and put in the work that it takes to feel good about things again. I would feel a lot of regret if I gave up on the relationship because of a breach of trust early on, as well as a lot of past issues in my personal life, when as a whole, being with my partner has been one of the most lovely and beneficial things for me, and I know we both feel really happy to be in each other's lives romantically.
This has been quite the explanation, but I think overall, I would be looking for some advice on how to set boundaries when dating someone who is new to polyamory (giving them grace while also advocating for myself), as well as dealing with the anxiety that's come up, and learning to get comfortable without feeling like something is sneaking up on me or I'm being thrown to the curb within the context of my relationship. And any other thoughts you might have while reading this, honestly! Also, it just helps to hear some kind words from someone not involved in the whole debacle, and to feel that kind of sense of community outside my polycule!

If I could go back in time in this situation, I would have advised against your agreement to “take things slow” because this is so individually variant. What is slow to one person is fast to another and that agreement really needed more concrete understanding behind it.

I think the result is obvious. They began “dating” and it came as a complete shock to you. I experienced similar things at times with previous partners. I would often describe the people they were seeing as “partners” or consider them as such but they did not feel the same. So it became very complicated.

The boundary wasn’t as explicit as it might seem to you from what you’re telling me here. It’s very hard to tell what “taking things slow” means to your partner or to the other person. In your discussions about what “dating” means, this is really clearly a bigger issue.

I also think that your partner is doing what a lot of people do in a lot of situations in non-monogamy, where one partner who is going out and dating is trying to reassure the other partner so much that inevitably the situation ends up agreeing to anything that will seem to calm their partner rather than asserting their own wants and balancing those with what their partner wants.

To continue to regard this as a violation of your trust, I don’t think is very fair. While I don’t doubt that you may feel like your trust was violated, this was a miscommunication and I feel like they should actually not be apologising to you specifically for violating trust and rebuilding trust when this was a result of not communicating meanings between one another.

The fact that it’s continued to be seen as a “violation of trust” I feel like means it gives it more meaning which continues to allow it to fester in your mind. I had a bit of a similar situation with a partner where we did not clarify what we felt “safe sex” was and my partner did something I felt was “unsafe”. It was hard not to feel violated and annoyed by it because what they did with someone else affected our sexual interactions — but in the end, it was a miscommunication rather than an error on my partner’s behalf.

It’s not surprising you feel a lot of anxiety if what you’re trying to negotiate is so unclear between the two of you. Have you sat down and talked about what both of you are interested in in terms of what your future relationship will look like? Have you agreed upon a set time that is yours and yours alone with your partner? I don’t think the issue is that your partner has less feelings for you, but it’s going to be very dissonant for you to tell yourself your partner loves you the same when you have no idea how the time they spend with you will change in the future.

It’s definitely possible that some of your underlying issues contribute, but I think the framing of this is also really important. The story we tell ourselves about ourselves is incredibly important. If we set ourselves up for failure in terms of what we think we’re capable of, sometimes that is actually the reason that we fail. Keep in mind, you’re trying a new relationship style which has no cultural script.

Even someone with “no issues” would experience anxiety going through this. It’s absolutely normal to be worried about being replaced and to have fears in these situations. It’s not because you’re inherently broken — but because you’re doing something that your society has likely not even told you is reasonable to pursue. Go easy on yourself!

I would suggest trying two different things: first, challenge your own framing of this incident. Do you have to call it a betrayal? Do you have to consider it a mistake which is entirely on the shoulders of your partner to fix? Can you reframe it as a lesson on how to move forward and clarify what things mean — especially when you start to have feelings about it? I think part of what’s keeping you stuck on this is the framing of it. This isn’t about blame, but about how you move forward.

Secondly, can you have more of a discussion with your partner about their time commitments? Can they give you an idea of what their ideal polyam setup is? Can you spend a little time thinking about yours — even if you’re monogamous? Is there a certain amount of time they can commit to giving to you and just only you — dedicated time that no one can interrupt unless it’s an emergency?

And finally, are you comfortable with having less time than you normally would in a monogamous relationship? One thing that is for sure is that you’re very likely not going to get as much time in this relationship as you would in another monogamous relationship. Is that okay?

And just as a final reminder, give yourself a little bit of grace here. You’ve got a brain designed to keep you alive and so much of what you’re doing right now you may not have seen any positive examples of. Take things one day at a time. I hope this helps and good luck!