something sad.

I have to leave home to go to school [and] start My New studies tomorrow. Actually, studying is not my favorite thing to do, but I really know if I want to earn big money in the future, I must study well now.
I think, maybe think my [new] classmates and friends can will (be able to) make me happy [cheer me up].

"Making someone happy" can be a rather strong expression. It sometimes implies a long-term kind of happiness or fulfillment in life, of the more idealistic kind.

The last clause is in a future tense because you haven't started your studies and so they're not your classmates yet.

<em>Here are some different ways to write this. </em>

something sad.

I have to leave home tomorrow to go to school to start my new program of study tomorrow. Actually, studying is not my favorite, but I really know that if I want to earn a lot of money in the future, I must study well/hard/a lot now.
Maybe think my classmates and friends can make me happy.