Polyamorous- partner started dating someone while we're in the middle of a fight

My partner Lucy and I got into a fight the day after I started my month business trip and we can't talk through our problems until I get home from this trip.

Before I left Lucy had started pursuing Fae for a few months and a few weeks into knowing each other they started dating but because of reasons I won't dive into they put their relationship on pause with the full intention of starting up again any time.

Last week I checked our shared calendar and saw Lucy had scheduled a date with Fae to make their relationship official and I was heartbroken because I had to find out through the calendar.

I'm conflicted because I fully understood and supported the two getting together but it feels like really bad timing because of our fight where I've already expressed to Lucy a fear of us breaking up over the fight.

I wish they would have waited until after our fight was resolved but I feel like I can't complain too much because the intention of dating was already made clear before I left and time can't stop just because I'm having problems.

I feel powerless and alone