Some people get over things by eliminating those things from their lives. He probably spends the vast majority of the days of his life over that whole experience. His rant was prompted by elements of that old world trying to intrude on the world he lives in now, which dredged up that negative energy.

Also, adolescents turn into adults, but they don't forget what passed before. So if you were evil to someone in high school, the adult thing to do would be to apologize if you're going to contact that person.