How do i know if a guy really likes me for me not for what i look like?

this guy in my cl used 2 pull my hair until i punched him then he stopped and not that long ago he choosed me 2 b his parter & we talk & he teases me a lot & he always asks me for a pencil and paper. & he tells me that he likes my clothes & he sticks up for me but he always sits w/ another girl but my sister says that he likes me and he's even helped me with stuff & he used to come into my work and just talk 2 me for 40 minutes but yeah i still don't know if he likes me or not. i kind of doubt it but you never know. and we have to sit together for 3 cles & when we do stuff together he always does the hardest part & he always encourages me. but then he goes 2 this other girl & sits w/ her during lunch & talks 2 her but she doesn't like him. and 2 make this whole thing worse my bf "loves him" but she always dissing him & if i told her that i liked him i would b dead. so my question is how do i get him 2 like me & how do i tell my bf that i like him? how do i tell if a guy likes me