This may sound surprising to you... but as I understand, in Buddhism the expectations like you described would be seen as your attachments and your ignorance.
Indeed, if you were infinitely wise, you would see this person as they are, and would not be mistaken by the appearance. The fact that your original opinion turned out to be wrong means you are not infinitely wise! :)
Two, once the expectations have been unfulfilled and you become disenchanted, to continue to be upset and to regret that things are not the way you thought they were, is a case of attachment. Meaning, you had one experience of the world, and now situation has changed - hence another experience, but you continue to hold to the past picture.
So in this way, these expectations are your ignorance and your attachment.