I slept with my best friends girl the night they broke up
You slept with your best friends girl. Why would you do that?
Because I like to hurt them.
You shouldn't so anything that would hurt people you care about. That's not a good friend.
I feel good because I made my best friend miserable.
That is not a nice thing to do something to someone you care about. That person trusts you. You should be honest with them and think about changing your ways.