(throwaway account)
I apologise for how unreasonable it all probably sounds. I haven't been dealing with the emotional turmoil too well, and I suppose I'd appreciate a reality check. (I'd also love to know if anyone here has ever gone through something similar.)

I'm a woman in my 20s, in a poly relationship with my NP for approximately a year and a half. Recently, my secondary partner ended our relationship (less than a year long), as he decided to be monogamous with his ex-girlfriend (something he had specifically told me he wouldn't do). I was devastated (though, of course, I could see it coming; not this specifically perhaps, but I could sense something was off). I've been pretty functional since then, mostly because I don't really have any other choice right now, can't really put my life on hold due to a break-up. However, I've found myself progressively losing the remnants of emotional stability, and for the past few days the pain and emptiness have been getting the best of me. I loved him so much, and I feel so unhappy despite trying not to. I can't stop thinking about how happy I was with him, how I would've liked it to go on forever, and - the worst of all - how jealous I am of his new partner, how much I want what she has. Stupidly, I can't get rid of the thought that he was the love of my life, the right person at a wrong time, all that cheesy nonsense.

I feel terrible just for thinking all that. It's deeply unfair to my NP, who I've been building a life together for multiple years now. (We've been having some non-poly-related issues lately, but the relationship is still solid.) What I felt for my ex-partner was special (obviously) and unlike anything else I've ever felt in terms of intensity. I could feel myself loving him more and more as time passed. I realise, of course, that it's infatuation speaking, plus the fact that we didn't really have the chance to face any serious issues stemming from the pressures of everyday life, cohabitation, etc. But it's like a hole I can't fill, and I can't stop thinking about what it would have been like to build a life with him. Every time I encounter some romantic content, a love song, anything of the sort, I can only think of him.

Of course, there's nothing to be done here anyway. The whole thing was bound to happen I suppose. I just hate the fact that I'm thinking and feeling all that insane stuff, and I'm worried it'll ruin what I have with my NP.

Some level-headed, outside perspective would be appreciated.