I took a pair of scissors and cut his bangs when he was sleeping
Why did you cut his bangs?
He had long hair since he was born and I've always hated him for it.
It's really mean to cut someone's hair without asking. He must have been really upset.  Was he?
I just wanted to help him realize that it's time for a change.
While it's understandable that you might not like the way someone looks, and would want them to cut their hair, it is wrong to change someone's appearance so drastically without their permission.  Imagine how you would feel if someone did anything like this to you.  Even if he looks better now, you still owe him an apology.