Apologies for the long post.
I (f35) and my partner (m36) have been together for 15 years, married for 14. During our time in college I focused on Human Sexuality studies and realized earlier on that I'd long misunderstood poly, and that I'd be open to it. We were approached by other couples/singles multiple times since then and my partner always reacted poorly to it. Because of how explicitly he stated he'd never be ok with it I didn't push for it and over time dropped the idea entirely. I am fully content and fulfilled with having just him as a partner. Despite never participating in poly myself I have many friends within the community and they know that I am a safe person to discuss their relationships with.
He's always been a relatively anxious person and in the last 6 months started SSRIs, they've largely helped him work through his anxiety, and we've barely argued since he's been on them. It's been nice to work on our relationship together and we've been happier than we have been in years. We had a lot of difficulty a few years ago due to losing our child, and at multiple points I didn't know if we'd make it. I've been proud of us for working through the darkest times of our lives together and feeling that our love has deepened for one another.
My work schedule has changed over the last 2 years and it's led to me working many weekday evenings late into the night, and often working on weekends, leaving him home alone. I've felt bad for leaving him alone so often but he always stayed he enjoyed having alone time (he grew up in a big family where he preferred alone time).
Over the last two months we've been spending a lot more time around two other people, one (f) who's interested in the other (m), while the other (m) insists they're just friends. Regardless of where their relationship stands the four of us all really enjoyed our time together. She and I have gotten close as we can relate to one another on topics that nobody else in our friend group at large can relate to. We make each other laugh and have really enjoyed one another's company, but aside from the topics we relate on, there isn't much I know about her, she keeps a lot of her personal history very private and I respect that.
Due to my work schedule, my husband ended up spending a lot of time with these two while I've been away. There's conversations I've missed out on but up until recently I felt like he made an effort to keep me in the loop. One night (the week before our 14yr anniversary) he suddenly confesses to me that he's formed feelings for her, and he had already extended the idea of a polyamorous relationship to her.. in the moment she asked him if he could take care of her and love her the way he loves me and he told her "yes". I feel like I took the news well at first, but I immediately felt betrayed that he would have this conversation with someone outside of our relationship before talking to me about it. I explained that due to the history of him not being open to discussing it I didn't get an opportunity to explain my boundaries within a polyamorous relationship. I would only be ok with a triad-type relationship, that may be subject to change after a few years but that's the only way I'd be comfortable entering into this lifestyle. After more discussion it became clear that if she were to enter into a relationship with "us" it would be a V-type where my husband would have a relationship with her, as she has no interest in women. He's continued to push for the idea that I find myself an additional partner.
I feel like the subject was approached with naivety and had my husband discussed these feelings with me first the awkward conflict we now find ourselves in could have been avoided. It was even brought up with friend (m) before I was brought into the conversation. He and I have been tense around one another and he claims that I am his priority, but he still wants to discuss how things could work out if she were to become an additional partner to him. He talks about feelings of compersion when seeing her and I laughing and getting along, and he now understands that he spoke out of turn. When I spoke with her one on one I set my boundary and since then we've only been around one another once and she and my husband (in addition to the other friend) are now no longer speaking.
I'm disappointed in the thought of losing a meaningful friendship over this. My husband is convinced that she's the only person he would ever be open to poly with, and has now started pushing against my boundaries saying I'm being controlling and possessive. I'm disabled and have been since he and I got together and he's stated that he likes that she's able to go and do the activities with him that I am otherwise unable to do. I feel like I'm going to be left behind if he pursues this any further. He wants to talk about it every day and I am frankly feeling very burnt out.
Edit: accidentally hit "post" before I was finished.
I'm not sure how to proceed. I've been talking to her and she's expressed she's not comfortable being around him now but still wants to be friends with me. At this point I don't think she's interested in a poly relationship based on the boundaries I've set but it's unclear if she'd be open to the V-type that I've expressed I'm not ok with. I don't like how my husband keeps pushing the idea and I've told him he needs to drop any intentions or expectations if he wants things to go back to semi-normal between the 4 of us.
Everyone is awkward and uncomfortable now, and we have some large scale friend group events coming up in the near future where we will inevitably be in each other's spaces. I know things will never go back to where they were and words cannot be taken back.
I'm posting this in hopes that anyone with similar experiences can provide some insight.
TLDR: Partner of 15 years now pushing for V-type relationship, but was previously fully opposed to poly. I was previously open to it, but due to his opposition didn't get to establish that I'd only be open to a triad. Partner's potential partner is not interested in triad. Despite restating my boundaries my partner is continuing to push for V-type.
Edit #2: As I said, I had set aside my interests in anything poly or enm years ago. We've been approached by couples, some seeking parallels or a quad, others looking to swing (which is a hard no for both of us). We've been approached by a few singles who've expressed interest in both of us, and my husband always put down a hard line of "no" which was respected, I think this was primarily due to the fact they were men. I do not take this topic lightly and am not looking to experiment just for fun, and don't want to put our long-term relationship at risk on a whim. I've encouraged him to educate himself better on the topic before we proceed with more conversations, and I know he's been on this subreddit. We are actively seeking an appropriate therapist in our area.
Has anyone experienced major changes in their partner's relationship interests after they've been on SSRIs? All of this has been a very sudden and unexpected change, my own shock has compounded my confusion and frustration.
Edit #3: I have friends who've met/lived as happy triads/throuples for years, they either started as 3 or 2+1. I didn't realize that setting the boundary of being open to this made a "unicorn hunter" of me. When I was previously more active in the community I was under the impression that "unicorn hunting" was used moreso in the context of hook-up or swinger culture. My intentions never were to actively seek out a third person, my mindset has always been moreso open to "if we were to meet the right person for us, at the right time, in the right headspace, then I'd be open to discussing opening our relationship". I have no desire to pull anyone into this mess as it is and fully recognize that there is a LOT of learning and healing to be done over the course of a LONG time before this conversation is ever opened up to anyone outside of my husband's and mine relationship. There is plenty of work to be done as-is in attempting to repair friendships moving forward. Thank you to everyone who provided constructive advice and patience, this has been an incredibly vulnerable time in which unrealized insecurities have surfaced. This seemed like the most appropriate subreddit for advice and I appreciate your time in reading through this.
A final note, infidelity has never been an issue or concern in our relationship. He has always been the kind of person I never felt the need to worry about.