My best friend has a boyfriend and I hate him.
Is there a reason you hate him?
I hate him because he stole my best friend away from me.
It's understandable to be upset that you're friend is spending more time with her boyfriend than with you. But, you have to remember that being a good friend means being there for her in all aspects of life. Try to compromise by offering friend nights where just the two of you hang out together.
No, I don't care. I want to hurt and get back him.
Friendships adjust and change and I understand why you're feeling the way you are. You need to try to be more supportive of your friend's relationship and perhaps you'll eventually realize her boyfriend is a good guy and not someone worthy of the hatred you're feeling. I would advise against doing or saying anything towards him as you might ruin your friendship.