>>724031975 (OP)
I like to think part of his vendetta was seeing Ness "replace" him with actual friends with the rest of The Chosen Four (starting with a girl no less) and became envious and spiteful.
He wasn't chosen, he's left behind like Naru from Sailor Moon except unlike Naru he chose to take action in a negative way.
Sure he didn't WANT to be chosen anyways because of the danger but it's not like he wanted to see the closest person he had to a friend just leave him and he did seek out grandeur possibly wanting to impress his dad as well given he accompanied him to Fourside.
I don't think Ness was the "unpopular" kid but his "friendship" with Porky probably did him no favors in socializing with others.
Had he not been so impatient or short-sighted or petty, he could've been a supporting friend to the Chosen Four ala Tony.
We know via Magicant that even if Ness' silence meant skepticism and hesitation, he truly wishes Porky was repentant and that whatever bond they did have could be salvaged.
It wasn't until he ran away from everyone in the end that made it harder and harder for him to be redeemed until he let himself age into the lonely, miserable monster he became.