Not alone, Kari!
I'm joining a triad that is currently going through this a fair amount. The two who've been in the relationship 12 years used to have good sex pretty often, and now hardly ever with their third having been in the relationship for a year. It's unsolved, as to how we handle it, but it's a big problem for the woman in the equivalent of your position. *sigh* In our case, it is looking like we're moving from poly-fi to more open poly, but I know that's not your preference.