Why does he treat me like this?

alright…so I’ve been friends with this family for quite awhile, going on nine years. so that means weve been real close since I was eight years old. theyre like my second family. my best friends moms boyfriend (who has been around the entire time) loves picking on me. he is 26. when im at the house he will punch me, tackle me, wrestle with me, tell me im grounded, steal my things and make me do ridiculous stuff, like rub his feet, to get my things back. and when im not at the house he will take my friends phone and text me off of it pretending to be her being mean, teasing me ect. were really close and I do tease him sometimes too. if he wasnt teasing me I would think somethings wrong. he treats my friend (his stepdaughter) like this too but no where near how he treats me. what I want to know is…what do you think he thinks about me??? does he consider me part of the family, like his own daughter. or does he not like me at all so picks on me 24/7. or do you think he is crushin on me??? advice please!!