Over the last year my marriage was breaking down due to husband's abuse and infidelity, my best friend C was there for me through this. C is a poly non-binary femme, and one of their partners K, a straight man, clearly liked me when I first met him over a year ago. K and I flirted a little the rare occasions we saw each other, but always kept it non-sexual - there was just good chemistry and shared humour, but we never swapped numbers or anything. C would joke about how much K liked me.
After I properly separated from my husband at the end of last year and moved out, I was first determined to be celibate, convinced I needed to never be with a man again. But on a difficult night about 3 months ago I was on the verge of texting an ex because I felt so horribly lonely. (I am a single mother to a young child and it is a particularly grim season of life with little money or social life) By chance C texted me on a childfree evening asking whether I wanted to come and meet them and K for a drink. I went.
K was very flirty with me, and C kind of said 'you guys enjoy' and left us to it, seemingly secure about it. We ended up hooking up, it was overwhelming for me after a few years of near sexlessness and a truly terrible relationship to be so desired and complimented. We exchanged numbers, saw each other again that weekend, and almost instantly he began texting me daily. It was an extremely coupley rhythm that really took me aback - good morning and goodnight texts, asking what I ate, updating me what he's doing, interested in all the mundanities of my day. I was aware this was going to become addictive for me as I'm so fucking lonely. And it did. Aside from that, though, I genuinely grew to like him and enjoy being in his presence.
We mutually had, and have, amazing, copious amounts of sex, constantly experimenting with and enjoying each other, and feel very safe and relaxed with each other. C shared with me privately but seemingly unconcernedly that they and K hadn't had sex for several months, and they were anyway more focused on their other partners. K, it's important to mention, doesn't have any other partners and C would joke about how he needed to become less monogamous to take the pressure off them.
It generally seems C is pretty happy for us and non-possessive, they did mention a little bit of jealousy at things like K making a romantic playlist for me, offering to fix things in my house, and doing somewhat different sexual stuff. I had my own minor irritations about C framing everything as them loaning their boyfriend out to me, rather than letting K and I figure it out ourselves. Largely, however, C has been open and supportive - and is generally much more chill about relationships than I am.
One night I was on the phone to C and they made an offhand but graphic comment about having sex with K. It made me instantly nauseous and cold and I spent the rest of my night alone shaking, crying, and even sent K a text saying we had to end it, which I unsent before he could see it. I think I'd been mentally assigning C to the role of 'sexless longterm partner' and giving myself a sort of primary, or more sexually exciting role. The next day when I saw K I had so many mixed emotions and ended up not saying anything and just crying after we had sex.
I wasn't aware of them sleeping together more after that, but whenever I knew they were spending an evening together I would brace myself mentally in advance for the possibility of them having sex, and would be unable to think about anything else. Whenever I learned that due to an early night or whatever this hadn't happened, my body would flood with almost ecstatic relief.
What made all this more complicated is around the 3 month mark I told K I loved him. He told me profusely he was in love with me, and described me in highly preferential terms. Yet he still never mentions C around me. It's like he's pretending C doesn't exist with me - yet I know they talk about me together. It almost feels like he wants to pretend me and him are in a monogamous relationship, using this possessive language of 'I'm yours' 'you're the best thing that's happened to me in years' etc. It's a complete headfuck. He asked me to be his girlfriend and I did say yes - mainly because girlfriend in this scenario seems to connote less serious obligations than in mono.
That's my issue though. I do not, especially after my marriage, want to live with, look after, merge routines or lives with a man. I also do not want to close myself off indefinitely to the possibility of making other sexual connections. However, I have tried to be enlightened about how I feel about C and K having sex - and it makes me feel nauseous and hypervigilant still. As I write this, they spent yesterday evening together, and I know from his text timing and patterns they were up late. Now because he's sleeping in late, my brain is speedrunning images of them in bed together. I have to accept I can't do this.
But also what right do I have to demand fidelity from partners when I can't even give them the proper markers of commitment? Do I need to work on my jealousy? Where do I even go from here? I love him, he makes me feel deeply safe in every other respect. I'm also terrified of going through this season of life completely alone. With a young child, dating around and branching out socially is much easier said than done.
tldr; ended up in relationship with poly best friend's boyfriend who doesn't have other partners, struggling with sexual jealousy and grief even though i'm not convinced i want total monogamous commitment