Everyone talks about the jealousy that comes with poly. Seeing your partner happy is difficult, but everyone warns you about it. The other part is seeing your partner sad because of a breakup.
And when that happens- so many feels. You feel bad for them, sympathy. You seem the emptiness in their heart, a hole that is no longer filled. You see the sadness, the lethargy. You see them shuffling around in slippers eating ice cream. You see that they're sullen and need alone time. You want to help, but you know you can't replace them. They held a special place in your loved one's heart, and now it's gone.
You feel helpless, but also a little schadenfreude. You let yourself think "I knew it!", before quickly putting the thought away, never letting anyone else know it was there, and trying not even to admit it to yourself. You have that little jump for joy that you'd never tell them, and then you feel guilty about having it. You know you're supposed to only feed sadness and empathy.
The books and articles told you about jealousy, but they never prepared you for seeing your loved ones have a breakup. They never prepared you for wanting to be close, but having your loved one feel cold and distant, or oscillating between being cold and extra needy. You never saw a breakup from the outside like this before, seeing it for the cold, lonely, ugly thing it is.
They never told you that breakups in poly suck.