How Do I tell if he likes me?

Well, theres this guy at school that I have liked for 4 years and never had the courage. The other day my friends bought it up and went over to him and asked him if he wanted to go out wif me. He sed no. My frends came back and sed he sed no but they sed hes probably doesnt wanna say yes infront of his mates. At school, he like teases me and has a nickname for me. But when I got to his house, he acts like hes my friend. But Im afraid that he likes this other girl, but he keeps denying it. WHAT SHOULD I DO?!?! AND HOW DO I TELL IF HE LIKES ME?!!?!?