A weird romantic triangle (or quadrangle?) with broken and reformed lines

[ladyhatshepsut.livejournal.com]

I read this story years ago and have been searching my files for several days for it, but it's been so long I can't even really recall what fandom it was. I thought I'd found it in a Criminal Minds/CSI Miami story but that wasn't it. To avoid more confusion on my part I'm going to use names instead of saying Person A, Person B, etc. but there's no guarantee that these are the ones in the story or that I'm using the right fandom. I'm just using couples I've seen in other fanfic stories and their tags.

Steve and Tony have been a loving couple for some time, seemingly happy together. Suddenly Bucky comes back in the picture (maybe or maybe not as Soldat first) and Steve leaves Tony cold for Bucky. After some time together (or maybe from the start) Bucky decides he wants to be with Natasha (either a new thing or getting back together) and he leaves Steve cold. Steve decides he loves Tony after all, but Tony, after a time of heartbreak, is now with Stephen and tells Steve to shove it. (Or maybe he has to think about that.)

Like I said, the story I'm searching for may not even be MCU/Avengers, that's just the main fandom I'm reading at the moment. If this seems familiar to someone in any fandom, please let me know. Many thanks.