This isn't a plot twist, it's plot armor protecting the MC.
It's not clever, it's a cop out. When you use betrayal like this, you are not testing a person's character, you're checking what you can get away with. An analogy for this would the psycho girlfriend on TikTok, the one who asks you the impossible question where you lose no matter how you answer. If you still trust her after that, you'll be tested again when she next feels insecure about things. The more you forgive, the more she'll push. Then she's shocked when she's pushed out the door.
You can't trust her because she doesn't trust you. It's not romantic, it's an origin story for an arch-enemy.