This is beautiful and touches on the reality of relationships, the belief that a person is always right without regard for what another person thinks.
Your main character was self-deluded and egotistic to believe her promotion had been on merit, not knowing Cynthia had stayed true as a friend.
This is what we do sometimes - live in a world of self-delusion believing we are right, not knowing we may be wrong. Nicely done.
Yeah, very correct about we humans. But there will always be that moment when one would have to take a step back and realize what's really going on.
We can only hope we do so sooner rather than later.