My (late 20's F) nesting partner (early 30's F) and I started dating a girl (late 20's F) three months ago.
The unicorn hunter red flags are going to go off as I describe this. My NP and I had been dating for years. Several months ago, I became friends with another girl through a shared hobby, and we got (platonically) very close. I introduced her to my girlfriend, and we all started to fall in love with each other from there, separately. We formed a polycule. None of us have had any prior experience with polyamory, which is likely another red flag.
Over the past three months, we've been dating, but earlier last week, my NP told me more or less that she was having doubts about the polycule and needed some space from our shared gf. I felt stuck in the middle. I couldn't enjoy company with either of them. I felt some resentment towards my NP, I felt like I was choosing between them when I wanted time with one or the other, and I felt like I was keeping a secret from our girlfriend.
Today, I was really not doing well, and I gently pushed my NP to be honest with our girlfriend about what she was feeling. The news was devastating to her, and it seems like things are over. We re-floated the idea of a V structure, but she wasn't comfortable with that for a few reasons. She doesn't even think the original friendship is recoverable, which was heartbreaking to me, but I'd never expect her to put in the effort after this.
It's really not my NP's fault... She can't help how she feels, and she *did* resort to honesty about her feelings as soon as she felt comfortable enough with it, but I feel embarrassed and betrayed, and I worry that losing this woman, friendship and all, will only breed more resentment toward my NP. And I worry she will resent me for pushing her to talk about it, if she wasn't ready or blames me for how it went. I think NP and I can recover from it, just, ugh. This hurts so damned much.
I don't know if I'm looking for comfort, advice, or a reprimanding, but it's all very fresh, and I feel heartbroken. I just want to know how to survive this. And I want everyone to be okay. I don't have a lot of people to lean on right now.
Edit to clarify:
I understand that my NP and I fucked up... dating as a unit is a mistake, at least with so little experience and so much room to grow with respect to direct communication skills. I want to clarify that from the start, I was always explicitly on board with the idea that if one of the dyads didn't work out, it didn't have to threaten the other two. Same for my NP. It is going to sound made up, but it wasn't all-or-nothing for us. Our partner was attached to the triad dynamic when we talked about it early on. She wanted the whole group to work. By no means does that make this her fault. We still failed her by dating her as a unit instead of nurturing our individual connections independently of one another before forming a group dynamic. We still got things ass-backwards.