What do you do if you know someone has a crush on you and you do too but you act like you hate them to impress your friends?

Stop it.

Your obviously gona hurt that person, then you are going to feel bad about it in the future.

If You like them as much as you say you do then you wouldn't pretend to hate them,

Friends, they come they go, Just Be Yourself Dont Be Afraid to speak what you feel.

:)