I'm thinking of being two faced towards a classmate.
Why do you want to be two faced?
It's the only way to maintain a social network
I think that's a pretty depressing view of the world.  You can maintain a far healthier social network by just being honest and getting your classmates to trust you.  I think you'll find you have much better relationships doing it that way!
But it's so much easier to pretend to like people.
Pretending that you like someone when you don't is really dishonest, and will just turn others against you. Your classmates aren't really going to want to be friends with you if they don't think you're trustworthy.