How do you know if a guy likes you?

im 13 yrs old in middle school and theres this guyi really like and i dont know if he likes me bcuz when we are around the pops (short for popular kids) he makes fun of me and only me but when we are hanging out with just my friends he id duper nice makes us all laugh! does this mean he might like me and how can i g et him alone without asking him to be alone by the way this also might help 2 yrs ago in elementary school we were really good friends and now all of a sudden last year (1st year in middle school) he started to constantly tease me and this year he makes me laugh and stil teases me also i have known him for about 7 years i am good at reading people usually but he is like impossible!!!!!!! help me please :p