Why do I remember this everyday?

A horrible thing happened to me in year nine that changed my life forever. Negatively but positively too. It was to do with school and these four people I thought i could trust pretty much tortured me and played mind games, ruined me psychologically. I think now because of them I have social anxiety. I remember it every day and the cruel things they did. Especially leaving me out in the rain in a t shirt. They never knew how badly it got to me. I got my revenge by succeeding in life and beating them in class and stuff. I'm over them I just can't believe it happened to me and I think about it everyday. Has it traumatised me? I used to get flashbacks and I used to lie awake at night crying for hours in the few months it was going on. I'm so much happier now but why do I keep thinking about it?