I seriously don't want my sister to go to the same college as me because she always like to cling to me.
It's your sister though. Why don't you want her to do that?
My sister is 5 years younger than me, she will ruin my social network
She can go wherever she wants. Colleges are big enough for the both of you.
I won't let her succeed, I'll make her misery when she is around me.
While you don't have to associate with her, you have no right to interfere with her life and make her miserable.