Hmmm, so how terrible was he that banishment was the answer and not actual parenting? From what was shown, none of it was worth a banishment. Yes, his treatment of his fiance was shit and punishment was deserved, like taking the crown away and giving it to his brother and making him do some sort of community service (or whatever the fiance's family called for) and taking his servants and nice things away. You know, like an actual punishment and parenting.
So my opinion so far is that this was the result of Bad "Parenting". The servants and tutors are not the people who should be correcting the "crown prince". They are there to serve there master and to teach Princely Duties (they do not have the power nor authority to do more). The parents are supposed to be the ones correcting bad behavior not the servants. Also the father hired a "decoy"(?) to flirt/seduce/have an affair with his son?! What?! Did I understand that correctly? If sex was involved (kissing is pushing it), I will be beyond disgusted. Also calling the fiance a "childhood friend" is also complete nonsense. Just because you set them up to marry as kids and forced them to "get along" that doesn't make them friends nor does it mean that they even like each other.
Sigh, okay most of my rant is over. Except, how old is FMC supposed to be? She looks like a child. The Prince at least looks his age. So what happened to her? This is assuming they are supposed to become a thing because I am not shipping him with a child.