I'm jealous of my best friend.
Why are you jealous of your best friend?
I used to be the smartest kid in my class for a few years, but my friend is smarter than me now. It made me quite jealous of him.
There will always be people who are better than us and that is okay. It would hurt your friendship if you are jealous of them.
It makes me angry to see him succeeding in life.
You should stop comparing yourself to him and be happy for him.  It isn't healthy to be jealous of other people and you should just focus on your own successes.