Help with my little step brother noooww!!! im gunna go insane!!!

ok. this mite tak a while lol so i have a step brother 3 years younger than me. he follows me EVERYWHERE no joke. i woke up and went into the kitchen so did he i do sumtin on my laptop he breats down my neak to watch. i go out side so does he ......and well i think you get the point and this morning he put his underwhere on me when i was sleepeing(eeeeewwww) and spilt sand and chips all over my floor please help he wont leave me alone.