How to make my younger brother happy?

Dear Cocos,

I am 22F and my brother is 14M. Sometimes we love each other and sometimes we hate each other. Once I got to know of his gf and adviced him a bit. At that point of time he was angry at me, but then kinda forgot about it.

Recently he has been moody and doesn't seems to be happy as before which is making me really sad. I am busy with my exam prep but try my best to spend time with him.

What shall I do to make him feel happy???? I have talked about this to my brother but he says everything is fine.