What do you think of me thinking I wasn't a selfish person?
Well, what made you change your mind?
I used to think I'd never be selfish or jealous or arrogant, but then I met someone that made me realise that I have can be all those things.
Most people can be selfish or jealous sometimes. It's good to realize when you behave in bad ways so that you can try to do better in the future.
That's the problem. This person has made me realized that I'm bad. I just want to hurt them now for making me realize that.
You shouldn't hurt them because they let you know that about yourself. It is good that you know now more about your shortcomings and limitations now and can do something about it.