Twilight is betrayed by her friends after they leave her, saying that Starlight was too much of a villain to be their friend. When Twilight's personality changed for the worst, Starlight takes the brunt of it after Spike runs away in fear.
When Princess Celestia, Princess Luna and Princess Cadance finds out about the betrayal, they confront the Mane 5 to get them to understand why Twilight is the way she is and why she is hurting Starlight.
Can Twilight be healed emotionally?
(Currently on Hiatus)