The love triangle in Wicked isn’t Fiyero choosing Elphaba or Glinda. It’s ELPHABA choosing Fiyero or Glinda
Elphaba’s decision to be selfish instead of selfless and going with Fiyero is a direct callback to Glinda’s selfish decision in Defying Gravity
Glinda chose to stay behind and get everything she’s wanted, putting herself over her friend
And then Elphaba does the same, choosing to be with Fiyero, putting herself over her friend.